The Reagan administration's efforts to win approval of a $100 million military and economic aid package for anti-Sandinista rebels was off to a rocky start yesterday, in part because of a Central Intelligence Agency document about a Nicaraguan "disinformation" campaign that caused confusion among the legislators it was designed to impress.

President Reagan has seen more than 60 members of Congress in two days in an effort to persuade them to support the package, but a White House senior official said yesterday that the private reaction of leaders had been "silence at best."

Senate Majority Leader Robert J. Dole (R-Kan.) said the administration had "a lot of work to do" to get the package passed and added that, "until the American people have a better understanding of this issue, it's going to be fairly difficult for many members of Congress to support it."

In another development, Oscar Arias Sanchez, president-elect of Costa Rica, who has been praised by Reagan administration officials, said he opposes military aid to the rebels, or contras, fighting Nicaragua's government.

"If I were Mr. Reagan, I would give that money to Guatemala, El Salvador, Honduras and Costa Rica for economic aid and not military aid to the contras," Arias said in a taped television interview on "John McLaughlin: One on One." "I don't think with that aid he is going to obtain what he wants."

But the biggest problem for the administration yesterday came not from Capitol Hill nor Costa Rica but from its own ranks. White House spokesman Larry Speakes declined for a second consecutive day to make the classified report about Nicaraguan disinformation public, and some officials said the document had clouded the renewed effort to obtain aid for the contras.

Some administration officials and lawmakers were privately critical of the tactics used by William J. Casey, the director of central intelligence, whom they said unwittingly had diverted attention from the aid request and toward the administration's tactics.

As recounted by participants, Casey showed up at a White House briefing Tuesday and passed out classified reports in brown wrappers on the "Sandinista Disinformation and Public Manipulation Plan."

The reports detailed an elaborate and sophisticated Nicaraguan plan to manipulate Congress and U.S. public opinion in favor of the Sandinistas and against the rebels. Among the elements of the plan was a Nicaraguan proposal to encourage network coverage of the Nicaraguan coffee harvest, an event that had already been depicted on NBC.

The report also said that U.S. church groups and such organizations as the Washington Office on Latin America would be used to widely publicize human rights violations committed by the rebels.

The Washington Office on Latin America yesterday issued a report, endorsed by three congressmen, that cited 139 cases of attacks against Nicaraguan civilians, 118 of which were committed by the contras and 21 by members of the Nicaraguan armed forces. A similar report recently was issued by Amnesty International and promptly denounced by Speakes.

But a report the same day from the National Endowment for the Preservation of Liberty, based on interviews with Nicaraguan refugees, painted a graphic portrait of Sandinista abuses, including "indiscriminate shelling of villages" and torture and killing of civilians.

A congressman familiar with both reports said that legislators of both parties were unlikely to be swayed by "propaganda" from either side. A senior White House official who briefed reporters on Reagan's trip today to Grenada acknowledged that the administration had put out "a half-story" on Nicaragua and expressed hope that a declassified version of the report will soon be made available.

In his trip to Grenada to commemorate the October 1983 invasion that he considers to be one of the foreign policy highlights of his administration, Reagan intends to draw a parallel between what happened on Grenada before the U.S. intervention and the situation in Nicaragua.

"You can see in Grenada the hijacking of a country by a small, dedicated, ruthless, violent band of communists and you can see that is what happened to the Nicaraguan revolution," the official said.Staff writer Joanne Omang contributed to this report.