The Reagan administration, responding to allegations that U.S.-backed Nicaraguan counterrevolutionaries were involved in drug dealing, acknowledged yesterday that some rebels "may have engaged in such activity" but said they were not acting on the orders of their leaders.

The administration's comments were contained in a three-page document delivered by Assistant Secretary of State Elliott Abrams to Rep. Charles W. Stenholm (D-Tex.). In a meeting with President Reagan last Thursday, Stenholm expressed concern about recent accusations that Nicaraguan rebel leaders misappropriated funds, tolerated human rights abuses by their followers and engaged in drug trafficking.

The document is the administration's first detailed public response to the allegations, which have been raised by conservative Nicaraguan and U.S. supporters of the rebels who are disaffected from some of the rebels' leaders.

The allegations have raised doubts about the integrity of the counterrevolutionaries, known as contras, at a time when the House is engaged in a prolonged battle over legislation to provide them with $100 million in aid.

The document cites "a limited number of incidents in which known drug traffickers have tried to establish connections with Nicaraguan resistance groups." It stresses that the incidents occurred during an 18-month period before June 1985 when the contras were receiving no U.S. assistance. The antigovernment movement, which includes an estimated 15,000 guerrilla fighters, was "particularly hard-pressed for financial support" at the time, the document says.

"Individual members of the resistance . . . may have engaged in such activity but it was, insofar as we can determine, without the authorization of resistance leaders," the document says.

The rebels thought to have engaged in drug dealing belonged to forces led by Eden Pastora, who has not received significant backing from the United States in almost two years. An official familiar with the administration's investigation of the accusations said Pastora has denied ordering drug deals or knowing about them.

Pastora is not a member of the main contra organization, the Nicaraguan Opposition Unity, which has come under scrutiny in recent weeks.

When drug dealers approached rebels in other guerrilla armies "they were turned down," according to Abrams. He said other accusations raised in recent days are "simply charges whose purpose is to defeat the contra aid proposals in Congress."

Stenholm said the report "does not end my concern" but said he is satisfied that the administration is conducting a thorough investigation.

The document also said that the contras' poor image in the area of human rights results from a campaign by Nicaragua's leftist Sandinista government to discredit them. It also says charges that contra leaders pocketed U.S. or private aid funds are "unsubstantiated," and that no U.S. assistance to the rebels has been diverted illegally.

A more extensive, classified dossier addressing the charges is being made available to members of Congress.