Nicaragua has reached an agreement with private bank creditors on a one-year deferral of $295 million in overdue loan and interest payments, a feat its officials regard as evidence that the U.S. economic embargo is increasingly meaningless.

Half the 130 banks involved are U.S. institutions and the rest are scattered among more than a dozen countries, said Richard S. Weinert, whose investment banking firm, Leslie, Weinert & Co. Inc., is financial adviser to Nicaragua's Central Bank. He said the agreement would be signed Monday in New York by officials of Nicaragua and the steering committee that represents the creditor banks.

"This is an important step because Nicaragua has consistently tried to maintain itself in good standing with the banking community despite great economic and financial pressure" from the United States, Weinert said.

Nicaraguan Ambassador Carlos Tunnermann Bernheim said the private debt, which totals $1.5 billion, was contracted by the government of Anastasio Somoza, which fell in 1979 to the current leftist Sandinista rulers. "Our political will is to honor all the debts and we are doing it within our economic capability," he said. The rest of Nicaragua's overall debt of $4.6 billion, which includes government-to-government loans, is not involved in the current rescheduling.

A senior Reagan administration official noted that the rescheduling involves no new funding. That indicates no improvement in Nicaragua's international financial standing, he said: "They're in default across the board and the banks are just trying to maintain some kind of claim on their assets."

Nicaragua began renegotiating its debts in 1980 and has since won favorable terms in two reschedulings that allowed it to defer all payments on the principal. It began deferring payments on all interest in June 1983, and many creditor banks have already written off the loans as losses.

Nicaragua's loan situation came under detailed discussion by administration officials last spring during internal debate that eventually led to the May 7 imposition of a U.S. trade embargo. At the time, a public denunciation of the debt and of Nicaragua as a "deadbeat" nation was discussed as a possible way to pressure and embarrass the Sandinistas. The option was rejected, according to officials involved, because many other nations friendlier to Washington are in the same situation and would also have been embarrassed.

The U.S. trade cutoff had no effect on the banks or on debt-renegotiation talks, which began last January, according to Marcos Wheelock, financial counselor at the Nicaraguan Embassy. "Even with these aggressions against Nicaragua, the banks are willing to cooperate with us in making easier terms," he said.

Weinert and other banking sources said the rescheduling covers all Nicaragua's past-due and maturing loan payments, totaling $295 million, through June 1986. Under the agreement, Nicaragua will pay $24.2 million on that amount in several installments. The Sandinistas made the first payment in March.

Nicaragua is the only Latin American nation that has an interest ceiling on its debt, and one of the very few having such favorable overall terms. The agreement negotiated in 1980 and still in effect gives Nicaragua a rate of 7 percent for about 65 percent of its debt until next December, with the difference between 7 percent and the market rate to be amortized and repaid between 1986 and 1989.

The new one-year deferral is deemed relatively short, and talks on further extensions are to resume next spring.