By ADAM NAGOURNEY, The New York Times

COLUMBUS, Ohio — Taking advantage of his financial edge, Senator Barack Obama is buying large amounts of advertising and building extensive get-out-the-vote operations in an effort to end Senator Hillary Rodham Clinton’s candidacy with twin defeats Tuesday in Ohio and Texas.

The intensity of Mr. Obama’s drive is especially apparent on television, where he has outspent Mrs. Clinton by nearly two to one in the two states. That is helping him eat deeply into double-digit leads she held in polls just weeks ago.

But after a month in which she raised $32 million — a remarkable amount, but still less than the $50 million or more brought in by Mr. Obama — Mrs. Clinton is fighting back.

The expenditures of the two Democratic presidential candidates, combined with a travel schedule that sent them and their surrogates from border to border in Texas and Ohio, reflect the expectation that the voting this week may be climactic. Mrs. Clinton’s advisers have suggested that she will bow out of the race if she falters in either state, after 11 straight losses.

Their face-offs are not just on television. Mr. Obama, of Illinois, has a town-hall-style meeting Sunday afternoon in Westerville, Ohio. Mrs. Clinton, of New York, just announced one there, too. Mr. Obama will be at Westerville Central High School, Mrs. Clinton at Westerville North High School.

Polls show that the race is deadlocked in Texas. Mrs. Clinton’s lead in Ohio has been whittled away, though she does still lead.

“Senator Obama is spending a lot of money on TV; if this can be purchased, he can win it,” Gov. Ted Strickland of Ohio, a Democrat who has campaigned across the state with Mrs. Clinton, said in an interview. “I think we’ve survived the initial blast of the Obama phenomenon, and we’re now holding steady.”

In a sign of Mr. Obama’s confidence and his strategy of amassing delegates wherever he can, he spent part of Saturday in Rhode Island, which with Vermont also votes on Tuesday.

Aides to Mrs. Clinton said she remained confident of winning the Ohio and Texas contests and would press on with her campaign, as signaled by her increasingly tough attacks on Mr. Obama.

But Clinton advisers have recently pointed to Mr. Obama’s financial advantage, in what appears to be an attempt to lay the groundwork to stay in the race should she lose by a small margin or squeak to victory in either or both states. “They are dumping a lot of money there,” said Mrs. Clinton’s chief strategist, Mark Penn, referring to the Obama campaign.

That said, Mrs. Clinton once enjoyed double-digit leads in both states, and her campaign had told supporters concerned about her string of losses that her effort to win the Democratic nomination would get back on track after solid wins in Ohio and Texas. Democrats said narrow victories there might not be enough to stanch a flow of uncommitted superdelegates — elected officials and party leaders — to Mr. Obama, who have until now deferred to the request by Mrs. Clinton’s advisers to wait for the vote in the two states.

Mr. Obama, campaign officials said, has spent about $10 million on television advertising in Texas since early February; Mrs. Clinton has spent just less than $5 million. Mr. Obama has spent about $5.3 million for television advertising in Ohio, compared with just under $3 million for Mrs. Clinton, the officials said.

Those figures do not take into account substantial advertising being presented for Mr. Obama by the Service Employees International Union. It also does not include money that Mr. Obama and Mrs. Clinton spent in Texas on Spanish-language television and radio stations in a competition for Latino voters, whom Mrs. Clinton had once considered an unassailable part of her base.

“I have many friends in Texas; I know your tradition and culture,” Mrs. Clinton said in one commercial broadcasting in Houston this weekend, speaking into the camera as subtitles translate her remarks into Spanish.

Mr. Obama’s financial advantage is helping him beyond the airwaves. His campaign flew 200 paid organizers from across the country to 10 campaign offices in Texas right after the Feb. 5 primaries, aides said, when some of Mrs. Clinton’s staff members were volunteering to work without pay. Another 150 were sent to build get-out-the-vote networks in Ohio, working for Paul Tewes, who was the Obama campaign’s director in Iowa. Mr. Obama’s eight-point victory in that state’s caucuses gave his campaign a huge boost.

Mrs. Clinton’s on-the-ground effort is no less aggressive and extensive; in particular, she has tapped into the network of support provided to her by Mr. Strickland. But in both states, her corps of workers are made up largely of volunteers. Many are from the two states, but others came here and to Texas on their own dime — typically from Washington and New York, some responding to an e-mail plea from Chelsea Clinton.

“We need as many people on the ground in Texas, Ohio, Rhode Island and Vermont as we can get,” Ms. Clinton wrote.

Mrs. Clinton and Mr. Obama were relying on surrogates to help carry their message ahead of the contests this week. Their identities offered a hint at the kind of voters both candidates were going after.

For Mrs. Clinton, it was Richard A. Gephardt, the former House Democratic leader from Missouri. Mr. Gephardt, a longtime opponent of trade deals like the North American Free Trade Agreement, was campaigning in the blue-collar Mahoning Valley in Ohio.

Mr. Obama has Arcade Fire, the popular indie-rock group who announced that the leading members would perform for him on Sunday at Stuart’s Opera House in Nelsonville. The city is not far from Ohio University and many of the younger voters that Mr. Obama seeks. (Aides to Mrs. Clinton, distressed that a band with many fans at the Clinton headquarters would join the line of supporters heading into the Obama camp, pointed out that the band was Canadian; in fact, while its members live there now, they grew up in Texas.)

If the Clinton and Obama campaigns succeed at their goals, every Democrat in the state will get a knock on the door from a supporter of one candidate or the other. Thousands of Mr. Obama’s supporters gathered Saturday morning at 75 staging stations.

In Texas, Mr. Obama’s campaign began the final part of its Caucus Education Program to make certain its supporters understood the state’s complicated voting procedure: a primary, in which two-thirds of the delegates are chosen, is followed by a caucus, which determines the remaining delegates. Volunteers went door-to-door leaving pamphlets that explained what the campaign had come to call the Texas Two Step, to remind Obama supporters that they had to vote twice.

Mr. Obama has repeatedly defeated Mrs. Clinton in caucuses. Because of that, his aides said, he could win more Texas delegates even if he lost the popular vote. Aides to Mrs. Clinton said Saturday that in part because of defeats she had suffered to Mr. Obama in caucuses, they had made an all-out effort to identify voters who would get out for both the primary during the day and the caucuses at night.

Here in Ohio, both candidates have focused on urban and suburban areas. Mrs. Clinton is also campaigning in rural areas and southeast Ohio, which she views as one of her strongest parts of the state. (Mr. Strickland did particularly well there in his election as governor.)

In Texas, both candidates staged last-minute efforts in Dallas, Houston and San Antonio, where both Mrs. Clinton and Mr. Obama had rallies Friday evening. Mrs. Clinton’s campaign brought in Mayor Antonio R. Villaraigosa of Los Angeles as part of an extensive roster of Latino surrogates sent across South Texas, reflecting the intensity of the struggle for those voters.

Mr. Obama focused on parts of the state with large concentrations of African-American residents, from Beaumont in East Texas to Houston, both with significant populations of evacuees from Hurricane Katrina.

Heading into the final days before the nominating contests this week, Mrs. Clinton and Mr. Obama used heavy television advertising to reinforce what had been the central closing themes of their campaigns.

Across Texas, Mrs. Clinton presented an advertisement that starkly suggested Mr. Obama was not ready to lead the world in dangerous times, echoing a similar charge she made against him Saturday in speeches in the state.

The Obama campaign began running a series of new advertisements in Texas over the weekend. Among them was a pointed response to Mrs. Clinton’s attack on his national security credentials, in which he criticized her judgment in voting for the resolution authorizing President Bush to proceed with the Iraq war.

Advertisements in Ohio reflected the prominent role that trade has taken here. Mr. Obama filled the airwaves with a spot saying he opposed Nafta, a pact put in place while Bill Clinton was president. Meanwhile, advertising in the state from Mrs. Clinton appealed to blue-collar workers by attacking trade and tax policies that she said unfairly protected corporations.

The extent of Mr. Obama’s financial advantage was increasingly clear this weekend and stirred concern among Mrs. Clinton’s supporters.

Mr. Obama has already begun spending money on staffing and television advertisements in some states coming up after Tuesday. Mrs. Clinton’s expenditures there have been minimal.

Clinton advisers said the television advertisement about Mr. Obama’s readiness for the White House — it features children sleeping while a narrator asks who would be better able to deal as president with a middle-of-the-night telephone call or a crisis — would be shown only in Texas. Part of that strategy was based on the calculation that the security message would resonate better in Texas than Ohio, where the economy is the overwhelming issue. But another aspect, an aide said, was that the advertisements would gain free coverage in the Ohio news media, saving money.

Financial concerns have also played into a decision by Mrs. Clinton’s campaign to buy time on the Fox sports channel to broadcast across Texas a town-hall-style forum that she will hold Monday near Austin.

Her aides said the venue was chosen in part to reach white male voters who had moved steadily to Mr. Obama. But the bigger factor, they said, was that the channel was a relatively inexpensive outlet.

Jeff Zeleny contributed reporting from San Antonio.