In the final three weeks of the recent election campaign, a seemingly desperate Rep. Joseph G. Minish (D-N.J.) pulled out the fund-raising stops in an attempt to hold on to his House seat, hitting up political action committees, fellow politicians and past contributors to amass a formidable supply of cash.

Already armed with $326,568 in the bank, the third-ranking Democrat on the House Banking Committee raised an additional $85,919 for a total of $412,487 cash on hand.

Despite a big last-minute advertising and get-out-the-vote campaign, however, the 11-term congressman lost -- and managed to spend only $142,958, according to his most recent report to the Federal Election Commission.

He thus ended up with $269,529 in his campaign treasury, according to the report. Under a special provision in the law, he can convert this political money to his personal use; all he has to do is pay taxes on it.

Minish won't say what he plans to do with the funds, but the big surplus has left a number of contributors to his campaign feeling that they were not giving money to help reelect him so much as to finance his transition to the private sector.

"They pleaded with me," one of the donors said. "Joe Puzo [Minish's executive secretary] called a couple of weeks before Election Day. He said Minish had a shot."

But Minish's Republican opponent, Dean A. Gallo, spent $337,431 in the closing weeks, much more than Minish, and beat the incumbent on Nov. 6, 128,000 votes to 101,000.

"We didn't send [the money] with the idea that he would put it in the bank. We sent it for the purpose of paying the expenses of the campaign," said Monroe W. Williamson, treasurer of the National Association of Retired Federal Employees Political Action Committee. "We don't want our money wasted."

Altogether, the retired federal employes PAC gave Minish $7,000, including $3,000 on Oct. 24, two weeks before the election.

Minish declined to respond to inquiries, but Bob Funesti, his press aide, quoted Minish as saying: "I have not made any decision, but whatever I do will be within the law." Funesti said Minish "spent as much as he thought he had to."

Funesti said Minish "has many options. He can keep it; it is a political fund, he can use it for political campaigns; he can make donations to charities; he can refund it." But, Funesti added, "it would be difficult to refund" because of the difficulties of deciding how much to give back to each donor.

Minish is one of many House members granted an exception from legislation prohibiting defeated and retired members from converting campaign surpluses to personal use. In 1980, Congress passed a bill prohibiting such conversions, but in a grandfather clause all incumbents at the time of enactment -- Jan. 8, 1980 -- were exempted.

In the past, other defeated and retired members have converted campaign funds into personal accounts, but the amounts were minor compared with Minish's $269,529.

Former representative Mendel Davis (D-S.C.), for example, converted $45,047 to personal use in 1981; Ed Beard (D-R.I.), kept $11,185; and Morgan Murphy (D-Ill.) in 1981 gave the FEC a report in which he listed $13,350 simply as a "closeout."

This year, in addition to Minish, other holders of large surpluses include Rep. Geraldine A. Ferraro (D-N.Y.), the Democratic vice-presidential nominee. She has a net surplus of $105,223 in her House campaign account, donated before she was selected for the national ticket.

An aide said, "I don't know what she is going to do with it," although it is possible she will use it in a campaign for the Senate seat now held by Alfonse M. D'Amato (R-N.Y.). He is up for reelection in 1986.

Minish's effort to raise money continued even after the campaign was over.

Funesti contended that there are additional debts to be paid, but Minish's report to the FEC lists no debts or other financial obligations.

The report lists receipt of more than $13,000 on four days -- Nov. 9, 15, 19 and 21 -- after the election. Among the listed post-election donors was a campaign fund run by Rep. Henry A. Waxman (D-Calif.) that gave $3,000 on Nov. 9, three days after the election.

Altogether, 13 of Minish's Democratic colleagues gave him money, including House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), $2,500; Majority Leader James C. Wright Jr. (D-Tex.), $3,000, and Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.), $1,000.

When told that Minish had ended up without spending $269,529, an incredulous aide to O'Neill said, "You're kidding, he's got all that?" and then started laughing. CAPTION: Picture, In unsuccessful reelection campaign, Rep. Minish raised $412,487, of which he spent $142,958. AP