Sen. Gary Hart (D-Colo.) is spending $115,000 a month in his quest for the presidency.

Unfortunately for him, it's being spent to pay off 1984 campaign debts, and he's still far from closing the books.

The debt from Hart's near-miss race for the Democratic nomination stands at $3.4 million. That's $900,000 below a year ago, but well short of the goal his fund-raising operation had set for 1985: to have it paid off by last fall.

"The debt has been a nuisance and an irritant," acknowledged William Dixon, Hart's administrative assistant, "but it has not prevented Gary from doing the things he wants to do."

Several Hart advisers who argued against his running for reelection to the Senate this year cited the debt. "I told him that he needs to be raising money in 1986, not spending it," said John Pouland. All insisted, however, that Hart's decision was not influenced by money.

Even so, Hart is said to understand that the longer the debt lingers, the more it will be a drag on him -- both financially and symbolically -- as he positions himself for another possible run for president. As the new front-runner for 1988, he no longer has the luxury of running the sort of renegade, low-budget, high-debt operation he put together in 1984.

"The thing about being out front is, you've got to look it," said one aide. In Colorado, the press has carried stories about the 340 small vendors (down from 750 at the end of the 1984 campaign) who are upset because they haven't been paid, or have been offered 50 cents on the dollar.

"Here's a fellow who is supposed to have new ideas," teased Howard H. (Bo) Callaway, Colorado GOP chairman. "It doesn't sound like a very decent idea to pay off these big bankers dollar for dollar at the same time you're sticking it to all these small businesses."

Dixon said that of the $3.4 million debt, $700,000 is owed banks on loans at a few points above the prime interest rate. The remaining $2.7 million is owed mainly to large creditors -- phone companies, advertising agencies, mail houses. Dixon said he expects them to settle at a heavy discount once the bank debt is paid off. "In reality it will take $1.25 [million] to $1.5 million to take care of the whole thing," he said.

Why has the exercise taken so long? Raising money to pay off a losing campaign is a notoriously tough political chore, and Hart has complicated matters by sticking to his 1984 pledge not to accept political action committee funds. On the other hand, he alone of the Democratic field in 1984 has emerged as a strong contender for 1988 -- and presumably that would give him cachet in money circles.

Critics suggest that Hart has never been sufficiently attentive to the money side of politics. "The key is the personal involvement of the candidate himself," said Bill Landau, treasurer of the Cranston for President Inc., who has seen his candidate reduce his 1984 debt from $1.4 million to less than $100,000. " Sen. Alan Cranston is on the phone all the time. I am not sure Hart has made that kind of effort."

Dixon counters that Hart traveled to 31 states in 1985 to raise money, and that the real problem last year was tactical. After knocking off about a third of the debt in the early part of the year with two mailings to the Hart "house list" of past contributors, which now has 115,000 names, Dixon said he erred by paying off his more insistent creditors, rather than using the money to finance more direct mail.

"I ate my seed corn," he said. There was also a "short disastrous adventure" last spring in which the Hart campaign spent $25,000 for a televised fund-raising appeal on Cable News Network -- which happened to start the day the TWA hostage crisis began. "It was a complete bust," said Dixon. "We pulled them after two days."

His appetite for unconventional fund-raising remains, however. This year, in addition to extensive direct mail, Dixon said he plans to test-market the sale of a "1985 highlights film of Gary Hart." He also expects to use Hart's Hollywood connections to raise money at movie premieres.

Meanwhile, each month the debt lingers, Hart must pay $40,000 in carrying costs -- about $8,000 in bank interest and the rest on staff, travel, mail, lawyers and Federal Election Commission compliance work. "He's very anxious we get rid of it," Dixon said.