Senator McCain advanced closer to the Republican presidential nomination in the much-vaunted Super Tuesday contests yesterday, but the result on the Democratic side was far murkier, all but assuring a drawn-out battle between senators Clinton and Obama.

Mrs. Clinton was the winner in New York, as well as California, New Jersey, Massachusetts, Arizona, Arkansas, Tennessee, and Oklahoma. Mr. Obama looked to be victorious in Alabama, Colorado, Connecticut, Delaware, Georgia, Idaho, Illinois, Kansas, North Dakota, and Utah. Early this morning, television networks projected Mrs. Clinton was also projected to win the California contest, though few actual votes had been tallied.

On the Republican side, Mr. McCain carried New York, along with California, New Jersey, Arizona, Delaware, Connecticut, Illinois, Missouri and Oklahoma. Michael Huckabee prevailed in his home state of Arkansas, as well as Alabama, Georgia, Tennessee, and West Virginia, while Mitt Romney won his home state, Massachusetts, as well as Minnesota, Montana, North Dakota, and the state that is home to his Mormon faith and where he oversaw the Olympics in 2002, Utah.

The rules for yesterday’s showdown in more than 20 states gave it the potential to be more decisive on the Republican side, where 10 states conducted winner-take-all contests that give the victor a state’s entire convention delegation even for a narrow win. The Democratic Party forbids winner-take-all primaries and requires a system that allocates delegates in proportion to the state’s popular vote or by congressional district.

For Democrats, Super Tuesday became a super standoff, with the two contenders each notching significant victories. Mr. Obama’s camp claimed an early lead in delegates awarded yesterday, but that was before results were in from key Western states such as California, where the former first lady was favored.

One of Mrs. Clinton’s most impressive wins of the night came in Massachusetts, where highly publicized endorsements of Mr. Obama by senators Kennedy and Kerry apparently failed to sway voters. Mrs. Clinton easily took the state, 56% to 41%.

Early in the evening, Mr. Obama posted an even more lopsided victory in Georgia, defeating Mrs. Clinton by 64% to 33%.

Mr. McCain had hoped to deliver a coup de grace to Mr. Romney in Massachusetts, but fell well short there. Meanwhile, Mr. Huckabee’s bid was showing more vitality than many analysts expected, as he performed strongly in states across the South. The Arkansas governor’s strength was also a blow to Mr. Romney’s hopes to emerge as the only viable alternative to Mr. McCain.

At a rally in Phoenix last night, Mr. McCain’s backers chanted “Mac is back,” as he somewhat reluctantly claimed the lead spot in the Republican contest. “We’ve won some of the biggest states in the country,” the Arizona senator said, cracking a rare smile. “Although I’ve never minded the role of the underdog and have relished as much as anyone come from behind wins, tonight I think we must get used to the idea that we are the Republican Party front-runner for the nomination for president of the United States.”

Mr. McCain also credited Mr. Huckabee for doing better than expected. “Not for the first time, he surprised the rest of us,” the senator said.

Mr. Huckabee told backers in Little Rock, Ark., last night that they had sent a resounding message. “Over the past few days a lot of people have been trying to say that this is a two-man race. Well, you know what? It is, and we’re in it,” he declared.

Despite his meager performance last night, Mr. Romney sounded upbeat and insisted he was giving no thought to withdrawing from the race. “One thing that’s clear is this campaign is going on,” he told a rally in Boston. “There’s some people who thought it was all going to be done tonight, but it’s not all done tonight. We’re going to keep on battling. We’re going to go all the way to the convention. We’re going to win this thing.”

In Manhattan, Mrs. Clinton delivered a stump speech to her supporters, making little comment about the night’s results, though she congratulated Mr. Obama on his victories. “I look forward to continuing our campaign and our debates about how to leave this country better off for the next generation,” the former first lady said.

At a rally in Chicago, Mr. Obama said: “There is one thing on this February night that we do not need the final results to know, our time has come. Our movement is real and change is coming to America.”

While Mrs. Clinton’s speech shied away from direct contrasts with Mr. Obama, he argued in blunt terms last night that he is more electable in November than she would be. “It’s choice between going into this election with Republicans and independents already united against us or going against their nominee with a campaign that has united Americans of all parties, of all backgrounds, of all races of all religions, around a common purpose,” he said.

The dead heat for the Democrats thus far left open the possibility that the contest might ultimately be resolved by the party leaders and officeholders known as superdelegates. They have favored Mrs. Clinton, but recently Mr. Obama has been narrowing the gap.

“We think this showing is going to help us continue to attract superdelegate support,” Mr. Obama’s campaign manager, David Plouffe, said.

As the Clinton and Obama camps waited for the polls to close, aides made the usual effort to downplay expectations about yesterday’s results. However, aides to Mrs. Clinton moved to stave off any talk of a decisive surge for Mr. Obama yesterday by repeatedly stressing that the contest is likely to drag on for weeks or months.

“The results are going to be close and, I think, inconclusive,” Mrs. Clinton’s communications director, Howard Wolfson, told reporters on a conference call yesterday afternoon. “The delegate process selection process is designed to keep the process going as long as possible unless you have an early knockout punch.”

Mrs. Clinton’s team also sought to move the focus beyond last night by announcing that she has accepted invitations to four debates in the coming weeks. They noted that there has been only one one-on-one face-off between the two Democratic senators.

Mr. Plouffe said Mr. Obama would take part in more debates, but he noted that the candidates would also have hectic travel schedule in the coming weeks. “We’ve done 18 debates and we did one last week,” the Obama aide said. “Our schedule is not going to be dictated by the Clinton campaign.”

Even before the polls closed yesterday, Mrs. Clinton’s allies in labor began looking down the road. In the past 48 hours, the American Federation of Teachers and the American Federation of State, County and Municipal Employees paid almost half a million dollars for pro-Clinton radio advertisements and mailings in Maryland, Virginia, Wisconsin, and the nation’s capital, according to filings with the Federal Election Commission.

Mr. Plouffe said Mr. Obama had clearly picked up momentum in recent days, but perhaps not fast enough for the onslaught of primaries yesterday. “We don’t have a big run-up here,” he said. “This was always a fairly daunting day for us.”

Few voting problems or irregularities were reported yesterday, though polls were reportedly held open for an extra hour last night in Alameda County, Calif., because of ballot shortages. Polls were also disrupted in some areas of Arkansas and Tennessee last evening, when tornados swept through the border area, killing at least seven people.

The first win of the day yesterday went to Mr. Huckabee, who prevailed after an unusual defection of Mr. McCain’s supporters at a convention choosing Republican delegates in West Virginia. When Mr. McCain’s backers saw Mr. Romney leading in the early tally, they moved en masse to Mr. Huckabee and gave him the edge to win the 18 of the state’s 30 delegates. Most of the remainder will be chosen at a primary in May.

In Georgia, Mr. Obama carried a remarkable 88% of the African-American vote, according to exit polls. He ran about even with Mrs. Clinton among white men there, while Mrs. Clinton picked almost two-thirds of white women.

In California, full results were not expected until the wee hours. An estimated 2 million people were to vote by absentee ballot, a figure that could amount to between 25% and 50% of the total vote. Many of the ballots were cast days or weeks ago, a fact that Mrs. Clinton’s supporters said could boost her result, as Mr. Obama closed the gap in California opinion polls only in the past few days. Another wild card in the Golden State was an unknown number of absentee ballots cast for John Edwards before he dropped out of the race last week. He had 10% in early California tallies last night.

While some saw signs in West Virginia and elsewhere of a secret pact between Messrs. McCain and Huckabee, the former Arkansas governor was still taking veiled shots at the age of the Arizona senator, who would be 72 upon entering the White House. “I bring the most in terms of experience, stamina, and preparation for the job,” Mr. Huckabee told CNN yesterday afternoon.