WASHINGTON -- New York Sen. Hillary Rodham Clinton yesterday pushed back hard against calls for her to withdraw from the presidential race, with aides saying she remains more determined than ever to remain in the contest until the end of the primary season.

Allies of Illinois Sen. Barack Obama have sought to increase pressure on Mrs. Clinton to drop out of the race in recent days, arguing that, because of his lead in pledged delegates, her only path to the Democratic nomination lies in a divisive campaign that drags to the party's convention Aug. 25-28 in Denver. Sen. Patrick Leahy, D-Vt., yesterday offered what may have been the starkest challenge to Mrs. Clinton from a prominent Obama supporter, saying in a Vermont Public Radio interview that she should avert a potentially bloody and ultimately futile battle by stepping aside.

Uncommitted Democratic leaders also stepped up their demands for a speedy resolution to the fight, arguing that the party cannot afford to be distracted from targeting the presumptive Republican nominee, Arizona Sen. John McCain. Democratic National Committee Chairman Howard Dean, in a round of television appearances, sought to calm increasingly anxious Democrats by setting a target date of July 1 for concluding the nominating process. Completing it sooner would be "all the better," he said.

The internal Democratic tumult over the battle, now in its 14th month, is the latest challenge for Mrs. Clinton. Her best hope for victory lies in extending the process until she can overtake Mr. Obama in the popular vote. She hopes to make strides in the 10 remaining contests, the biggest of which are Pennsylvania on April 22 and Indiana and North Carolina on May 6.

Yet since winning the mega-prize state of Ohio on March 4, Mrs. Clinton has given no signal that she is considering dropping out. Campaign advisers said the pressure has only hardened her resolve and created a backlash among supporters who feel that she is being unfairly attacked.

To counter the impression that Mrs. Clinton is prolonging the race, her campaign has begun describing what they say is a pattern of trying to force her to "the sidelines" every time she appears on the verge of victory. In an e-mail to her supporters, Mrs. Clinton asked: "Have you noticed the pattern?"

"Every time our campaign demonstrates its strength and resilience, people start to suggest we should end our pursuit of the Democratic nomination," she wrote. "Those anxious to force us to the sidelines aren't doing it because they think we're going to lose the upcoming primaries. The fact is, they're reading the same polls we are, and they know we are in a position to win."

At a rally in Indiana yesterday, Mrs. Clinton raised the prospect of quitting in front of more than a thousand enthusiastic supporters. "There are some people who are saying, 'You know, we really ought to end this primary; we just ought to shut it down,' " she said at a high school near South Bend.

"No!" the crowd shouted back.

Mrs. Clinton continued: "There was a poll the other day that said 22 percent of Democrats wanted me to drop out, and 22 percent wanted Senator Obama to drop out. And 62 percent said: Let people vote."

But other recent polling has found Democrats' appetite for the extended campaign beginning to wane. A Pew Research Center survey released this week found 44 percent of Democratic voters believed that the extended campaign fight is a "good thing" for the party, down from 57 percent in late February.

Responding to a comment from Mr. Obama that the Democratic primary race was like a good movie that had gone on too long, Mrs. Clinton replied: "I like long movies."

Calls for her to withdraw only lead to "a greater determination," Clinton spokesman Jay Carson said. "When the punditocracy has declared her dead, voters have said, 'Hold on just a second.' It has happened three times. And three times, she has proven them wrong."