President Carter is destined to be 1980's long distance runner, wobbling toward the convention laps ahead of his challenger, lacking in style and steam but still so far ahead that he probably cannot be caught.

Mathematics, not momentum, is what propels him now. Carter will probably reach the convention finish line first -- but the question that remains is whether, when he gets there, he will have enough strength left to break the tape.

Sen. Edward Kennedy's strategists have hoped to soundly defeat the president in the last round of primaries and then, if Carter still has enough delegates for a first ballot victory, to perhaps force a convention rules fight that would free delegates who are now legally bound to vote for Carter in the initial ballot.

Many Democratic Party pros doubt that the convention will go along with such a change, and some of the doubters are Kennedy liberals. But there are still a few prominent Democrats who question whether a wobbly president will be able to hold all of his delegates in line. And the is just enough hope to keep Kennedy running, and to keep his planners planning, even as the president heads into the home stretch of his own long distance run. e

Yesterday's votes in Pennsylvania, Missouri and Vermont gave Carter a further push, and cost Kennedy more ground in the delegate race, where he was already trailing badly.

Kennedy had started the day needing to win 65.8 percent of the delegates in all the remaining primaries and caucuses in order to stop a first-ballot Carter victory according to calculations by Carter delegate-counters, whose figures are very close to those of their Kennedy competitors. Any time Kennedy fails to reach that 65.8 percent target it means his requirement is even higher for the next contest.

That is why the mathematics of 1980 are now so heavily against Kennedy's coming all the way back in time for a first-ballot victory of his own at the August national convention in New York. Kennedy strategists hope for an overwhelming victory on the big final primary day of June 3, when nine states vote, including delegate-heavy California, New Jersey and Ohio. n

But before Kennedy gets to June 3, he must run through May, which features a number of contests in states that are mostly Carter country -- among them Texas, North Carolina, Tennessee, Arkansas and Kentucky.

The Kennedy plan, predicted on a strong win in Pennsylvania, was to batter Carter in the final round of primaries and then perhaps force the convention rule fight. The hopes that Carter would look so bruised and the partly so disaffected with his policies, that those originally committed to him would swing to Kennedy.

But Kennedy's problem is that he must first catch Carter while running uphill in the delegate race. The Carter delegate-counters, figuring what they call the president's "worst case scenario," estimate that after the four primaries on May 6 Kennedy will need to win 79 percent of the remaining delegates in order to stop a first-ballot Carter victory. By the end of May, they estimate, Kennedy will need 88 percent of the delegates who are at stake in the June 3 primaries.Carter would need just 18 percent of those delegates -- a figure that the president is certain to reach.

As Carter heads to the June 3 round of primaries, his greatest difficulty may be more financial than purely political. As of last night, according to Carter campaign manager Tim Kraft, the campaign will have spent "in the $13 million range." The campaign is allowed to spend $19 million total through the convention.

Kraft said that Carter will not spend in May at the past rate of $2.5 million a month. In this way, he said, Carter will be able to spend adequately for media in the June 3 primaries.

If Kennedy goes ahead with the fight to change convention rules binding delegates on the first ballot, the effort is sure to meet with mixed reviews within that broad segment of the Democratic Party outside the Carter inner circle.

Ray Majerus of Wisconsin is regional director of the United Auto Workers, a Carter man, even though his union has provided strong backing for Kennedy. He will not go along with an effort to change the rules at the convention in order to prevent Carter from winning the nomination.

"The ball game just doesn't get played that way," he said. "No one's going to say that we are going to jump from the winner to the loser just because the winner has gotten a black eye or two at the end."

Rep. Tom Harkin of Iowa is a liberal Democrat and Carter backer who says he might be willing to vote to change the rules in order to permit people to switch from Carter to Kennedy.

Harkin said he canvassed his state's delegates now bound to Carter and found mostly disillusionment. "I never talked to one person who told me point blank that . . . Carter had done a great job," Harkin said. " . . . I found a lot of the opposite. I did find some who wished they'd gone for Kennedy earlier."

Sentiments like this keep Kennedy running, even when the mathematics say he cannot win.