Gary Hart for President is alive and resuscitating in the bracing primary air of New Hampshire.

The candidate for the Democratic nomination is in the pink. His spiel is more spirited, his message more compelling and his audiences more responsive than before.

But his campaign is in the red.

Miscalculations led him into costly, losing straw-poll efforts that were never budgeted and that badly tarnished his reputation with party pros and potential contributors. Sen. Gary Hart (D-Colo.) is banking on a flurry of fund-raising events to get him into the black by June 30, when all campaigns must report on their fiscal health for all to see.

Still, his view remains rosy. Hart tells audiences that he will be their next president and that the race for the Democratic presidential nomination will come down to two finalists, Hart and either former vice president Walter F. Mondale or Sen. John Glenn (D-Ohio)--"I'm not sure which."

There was no evidence of damage from Hart's well-publicized, unsuccessful presidential straw-poll efforts in Massachusetts and Wisconsin as he rolled through a visit several days ago to the state where the nation's first presidential primary traditionally is held.

His supporters were enthusiastic as he opened his headquarters in Concord; teachers, labor leaders and just plain folks pronounced themselves impressed with what he had to say at rallies; local media coverage was extensive when he toured a toxic waste site and held forth on the horror of it all.

But perhaps there was evidence of the fallout from the straw polls when he hit New York City. His campaign managers had hoped to raise $20,000 to $25,000 at a fund-raiser at the home of Loulette and Howard Samuels, the chairman of the National Soccer League and a prominent New York Democrat. But they netted, by their own count, just $10,000.

Hart, meanwhile, appears to have come away from his latest encounter of the third-place kind in Wisconsin with new resolve.

In what could be crucial to his chances, he voiced confidence during an interview that he can capture the nuclear freeze issue, which so far has helped to bury him in these early tests, and make it his.

So far, the nuclear freeze issue has launched the candidacy of Sen. Alan Cranston (D-Calif.), who has ridden it skillfully through the straw polls, culminating in his victory in Wisconsin, where Hart finished a distant but respectable third. What hurts Hart most, he said, is that he thinks that, by rights, the nuclear arms issue should be his because his is the most comprehensive proposal. It is also the most unilateral.

In an interview the other day, Hart said he believes that the United States should take these unilateral steps to ease the arms race:

(1) Do not build the MX missile; (2) do not build the B1 bomber; and (3) Congress should enact a law that would take the "build-down" proposal that President Reagan reluctantly has embraced as a negotiating formula and make it America's unilateral policy. That would require the United States to destroy two nuclear launchers or warheads every time it deploys a new one--regardless of what the Soviets do.

A few days ago, Hart made his bid for the arms control issue as he stood under a spreading maple tree on the front lawn of New Hampshire's politically redoubtable Dudley Dudley, the top Democrat in the state government.

"I have challenged every Democratic candidate for the presidency to come forward with specific proposals," Hart told a rally of about 100 people, most of them pro-freeze, " . . . not only to freeze the production and deployment of nuclear weapons, but to sharply and dramatically reverse the nuclear arms race, and to introduce steps that will prevent the accidental or miscalculated use of nuclear weapons."

Hart, whose proposal addresses all that, added this jab at Cranston: "We cannot wage this campaign successfully with generalities and rhetoric and simple slogans."

Later, in an interview, Hart states it specifically. His tone is carefully low-key as he talks of the politics of the freeze and hits at Cranston's support of the B1 bomber, which is built in California, and of the resolution of Sens. Henry M. Jackson (D-Wash.) and John W. Warner (R-Va.), which provided for a mutual nuclear weapons freeze--but only after a buildup of nuclear weaponry.

"There are people who only care about the freeze," Hart said, "and who would almost resent it if a candidate talked about anything else--any other message, economic or environmental . . . . Mondale and Cranston and I are the only ones talking about the freeze. Mondale and I are talking about other things as well--and I think that gives Alan a certain advantage. He just goes to them and says, 'The freeze is all I care about,' in effect.

"I think Alan, down the road, will have to account increasingly--and I'm saying this not as an adversary but as more of an analyst, in a detatched way--for his B1 position and his support of Jackson-Warner. Those do cloud the purity of his message."

As Hart strives for the political lead on arms control, he would go further than the build-down proposal that Reagan has made part of the U.S. negotiating position. He would implement it unilaterally.

And what if the Soviets continue to build up?

"We would just be establishing by law a process that is in practice now," he responded. He conceded that the current practice of modernization and retirement of outmoded weapons is not the same as a flat one-for-two replacement, but added: "The goal is deterrence. It's not a function of the overall numbers, but of survivability."

In politics, however, survivability is a function of numbers--of dollars and votes.

"The only thing that could cause me to drop out of the race would be if there just was no money to finance it," Hart said. "And I am convinced that we will have enough funds."

He also never anticipated that his campaign would be in debt so early.

Hart's advisers had planned to begin their direct-mail funds solicitation in May but couldn't cover the $50,000 cost of sending 120,000 letters. Now they say they will mail in July, which is a costly delay because it means they must mail during the summer doldrums. But it is necessary to begin now so they can reinvest the proceeds in the hope of reaping a large direct-mail dividend by the end of the year, when federal matching funds will be calculated.

This is a political life cycle with which Hart, 45, is familiar.

"We were always spread terribly thin in 1971," he said, recalling his days as former senator George S. McGovern's presidential campaign manager. "It was razzle-dazzle to create the impression of a big nationwide campaign. This time it will be different. We are in it for the long haul."