Mel Nasielski of Allan & Nasielski, a Philadelphia direct-mail firm that does political work for Democratic candidates, on Thursday bought Gary Hart's 1984 contributors list for $6,500 at an auction conducted by the U.S. Marshal's Office in San Francisco. Nasielski was the only bidder.

The list, on a computer tape and containing the names of more than 40,000 donors to Hart's cause, was ordered seized for auction by a U.S. district court judge in early July.

The money it brought at the auction is to be used to help pay off a $140,000 debt owed by Hart's 1984 campaign to Tri-State Envelope Corp. of Beltsville, Md.; the company made about 10 million fund-raising envelopes for the campaign. Tri-State said it had hoped the list would sell for as much as $30,000.

Nasielski, who read about the auction in a trade journal, said he plans to market the list to presidential candidates and candidates for other offices. "I hope I got a bargain," he said.

Meanwhile, Tri-State and Semper-Moser Associates, which claims it is owed $165,000 for television spots purchased for the 1984 Hart campaign, went to court Friday in an effort to claim that $100,000 in Hart campaign assets on deposit in a Denver bank can be used to pay off part of Hart's 1984 campaign debt immediately.

Hart's creditors and the 1988 Hart organization disagree over how the $100,000 certificate of deposit, which was purchased by the 1988 campaign, can be used.

Creditors say that certificate of deposit can be applied to the old debt, while campaign officials say the 1988 contributions must first be used to retire 1988 campaign debts. U.S. Magistrate Richard B. Harvey in Denver said he will rule in a few weeks on whether the certificate of deposit is 1984 money or 1988 money.

Michael R. Moore, treasurer of both the 1984 and 1988 campaigns, testified that the defunct '88 campaign has $123,000 in the bank, enough to cover the 1988 debt of $99,000. The 1984 debt is $1.3 million.

The Federal Election Commission, however, has not agreed so far to a request from the 1988 campaign committee to divert funds to the 1984 debt.