WASHINGTON — Hillary Rodham Clinton scored comeback primary wins in Ohio, Texas and Rhode Island Tuesday night, denting Barack Obama's delegate lead in a riveting Democratic presidential race. Arizona Sen. John McCain, an unflinching supporter of the war in Iraq, clinched the Republican nomination.

Clinton's three triumphs ended a month of defeats for the former first lady, and she told jubilant supporters, "We're going on, we're going strong and we're going all the way."

Obama won the Vermont primary, and sought to counter Clinton's claims that the night had been a race-altering event. "We have nearly the same delegate lead as we did this morning and we are on our way to winning this nomination," he told supporters in Texas.

The two rivals also competed for support in caucuses in Texas that began 15 minutes after the state's primary polls closed.

Both Democrats called McCain — a Senate colleague — to congratulate him on his triumph in the Republican race.

The 71-year-old Arizona senator surpassed the 1,191 delegates needed to win his party's nomination, completing a remarkable comeback that began in the snows of New Hampshire eight weeks ago. President Bush invited him to lunch — and an endorsement — at the White House on Wednesday.

"We are in Iraq, and our most vital security interests are involved there," said McCain at a victory celebration nearly a decade in the making.

McCain's last remaining major rival, former Arkansas Gov. Mike Huckabee, conceded defeat after a campaign that included a stunning victory in the leadoff Iowa caucuses on Jan. 3. "My commitment to him and the party is to do everything possible to unite our party, but more important to unite our country so that we can be the best we can be," Huckabee said in Irving, Texas.

Clinton won the Rhode Island primary with more than 58 percent of the vote.

But Ohio and Texas were the big trophies of the night, rich in delegates and — according to Bill Clinton — must-win states for his wife.

Her share of the Ohio vote was 55 percent in nearly complete returns, and she was winning nearly 51 percent in Texas.

Obama was gaining roughly 60 percent of the Vermont vote.

In the four-state competition for delegates, Clinton picked up at least 100, to at least 77 for Obama. Nearly 200 more remained to be allocated for the night, 163 of them in the Texas primary and caucuses.

Obama had a total of 1,466 delegates, including separately chosen party and elected officials known as superdelegates, according to the Associated Press count. He picked up three superdelegate endorsements Tuesday,

Clinton had 1,376 delegates. It takes 2,025 to win the nomination.

With their remarks, first Clinton, then Obama, sought to frame the race in the best possible terms for their own campaigns.

"They call Ohio a bellwether state, the battleground state. It's a state that knows how to pick a president and no candidate in recent history, Democrat or Republican, has won the White House without winning the Ohio primary," the former first lady said in Columbus.

Moments later, Obama stepped to the microphone in San Antonio. He said the outcome of the Texas primary might not be known until Wednesday, and he all but conceded defeat in Ohio. Either way, he added, it was the delegates that mattered.

Clinton and Obama spent most of the past two weeks in Ohio and Texas in a costly, bruising campaign, with the former first lady questioning his sincerity in opposing NAFTA and questioning his readiness to serve as commander in chief.

Polling place interviews with voters in both states suggested the criticism hit home, showing Clinton was winning the votes of late deciders in Ohio and Texas, as well as Vermont.

Hispanics, a group that has favored Clinton in earlier primaries, cast nearly one-third of the Election Day votes in Texas, up from about one- quarter of the ballots four years ago, according to interviews with voters as they left their polling places. Blacks, who have voted heavily for Obama this year, accounted for roughly 20 percent of the votes cast, roughly the same as four years ago.

The economy was the No. 1 concern on the minds of Democratic voters in Texas, Rhode Island and especially in Ohio. But in Vermont, almost as many voters said the war in Iraq was their top concern.

More than three-quarters of Ohio Democrats said international trade had cost their state more jobs than it had created.

Roughly six in 10 of the Democrats who were questioned outside the polls Tuesday said that so-called superdelegates, who are party officials, should vote at the national convention based on the results of primaries and caucuses. That was unwelcome news for Clinton, who trails Obama among delegates picked in the states but holds a lead among superdelegates.

Obama had campaigned hoping to land a knockout blow. As of March 1, his campaign had spent about $9 million on television advertising in Texas and about $4.5 million in Ohio; Clinton had spent about $5 million in Texas and about $2.3 million in Ohio, according to TNS Media Intelligence/CMAG, an ad tracking firm.

Clinton showed no sign of surrender as she campaigned on Tuesday. "You don't get to the White House as a Democrat without winning Ohio," she said in Houston.

"My husband didn't get the nomination wrapped up until June (in 1992). That has been the tradition," she added, without mentioning that this year most primaries were held much earlier than in 1992. "This is a very close race."

For his part, Obama was already advertising in Mississippi, which holds its primary next week, and planned trips there and to Wyoming, which has weekend caucuses.

Pennsylvania, the biggest single prize left, holds its primary on April 22.

"All those states coming up are going to make a difference," he said. "What we want to do is make sure we're competing in every single state."

It takes 2,025 delegates to win the Democratic nomination, and slightly more than 600 remained to be picked in the 10 states that vote after Tuesday.

The Democratic marathon was in contrast to a Republican race that was fierce while it lasted but had long since been settled.

McCain's campaign nearly imploded last summer. But he regrouped, reassuming the underdog role that he relishes, and methodically dispatched one rival after another in a string of primaries in January and early February.