Sen. John Kerry cemented his position as the Democratic front-runner by rolling to victories Tuesday in Missouri, Arizona, and three other states, winning the bulk of delegates in the biggest day of presidential balloting. Sen. John Edwards easily captured South Carolina, keeping his White House hopes alive.

In Oklahoma, retired Gen. Wesley Clark claimed a narrow victory over Edwards, but returns were not official. Clark finished a distant second place, behind Kerry, in Arizona and New Mexico.

Sen. Joe Lieberman of Connecticut, the 2000 vice presidential Democratic nominee, quit the race after going zero-for-nine in the primary season and finishing far back on Tuesday.

“The judgment of the voters is now clear,” Lieberman told chanting, clapping supporters at a hotel ballroom in the Washington, D.C., suburbs.

He wished his rivals well then said, “For me, it is now time to make a difficult but realistic decision. After looking at the returns and speaking with my family and my campaign team I have decided tonight to end my quest for the presidency of the United States.”

Former Vermont Gov. Howard Dean, a commanding front-runner in the contest just three weeks ago, finished far out of contention in the seven states and was fighting to keep his hopes alive until a make-or-break test in Wisconsin on Feb. 17.

National showing

The result of Tuesday’s balloting, the biggest voting day of the fledging campaign season, was to boost Kerry’s already-strong momentum and increase his count of delegates to the Democratic nominating convention this summer.

With his victories in Arizona, Delaware, Missouri, New Mexico and North Dakota, Kerry made his first display of national strength.

“I pledge to you tonight,” Kerry told supporters, “I have only just begun to fight.”

In early January, Kerry stopped campaigning everywhere but Iowa in a do-or-die strategy that paid off handsomely when he won the caucuses in that state and, a week later, the leadoff primary in New Hampshire.

Kerry on Tuesday called his Missouri victory “fabulous,” emphasizing his main goal of the night was winning delegates. There were 269 up for grabs, one-tenth the number needed to win the Democratic nomination. Together, Missouri, Arizona and Delaware accounted for 134, or almost half the day’s total.

For Edwards, Tuesday’s goal was more basic: survival.

The senator had said for months he needed to win South Carolina, where he was born, to continue his presidential campaign. By doing so — handily — Edwards left himself well positioned for the next two Southern primaries, in Virginia and Tennessee, next Tuesday.

“Tonight, we stand at a crossroads,” an exuberant Edwards told a crowd of several hundreds supporters at a nightclub in downtown Columbia, S.C. “If the American people give me a shot at George Bush next November, next November I will give them back the White House.”

Exit polling

Interviews with voters as they left the polls in three of the states voting Tuesday showed different strengths — and potential vulnerabilities — for the top finishers.

Kerry, a member of the U.S. Senate for 19 years, won in several states among voters who wanted a candidate with experience, or who put electability at their top of their priority list.

In South Carolina, Edwards’ victory was powered by his strength among the state’s more conservative and older voters. He also won among voters who said they most valued a candidate who cares about people like them.

Edwards and Kerry ran about even among blacks, each winning about a third of the vote.

The Rev. Al Sharpton of New York, the sole black candidate in the field, won only about one in five black votes, despite his intensive efforts in the state. Blacks made up about 45 percent of the South Carolina electorate in Tuesday’s primary, by far the largest minority turnout of any state that has voted so far.

In Oklahoma, the candidates largely split up the support among various demographic groups, reflecting the close order of finish.

Even as Tuesday’s balloting was under way, Kerry was looking ahead to Saturday’s next round of voting in Michigan and Washington state.

“When you’re running for president of the United States, I think you have to run nationally, I don’t think you can cherry pick,” Kerry told reporters, aboard his chartered Boeing 737 as he flew to Spokane from Phoenix.

Even as the victories roll up, he insisted, he would continue to campaign “in high cylinder, high gear.”

“We’re not playing cautious here,” he said. “We’re fighting to win this race.”