President Reagan summoned more than a dozen House Democrats to the White House yesterday to lobby for his $100 million aid package for Nicaraguan rebels, while his top advisers met late into last night with members of Congress working out the details of a possible compromise.

The compromise being worked out would delay the implementation of the aid for 90 days while a diplomatic solution to the Nicaraguan conflict would be sought, administration sources said. However, the 90-day period would not be written into the legislation but would be implemented instead by a presidential executive order. Under this plan, Reagan would promise to delay the aid in a message to Congress before the vote and then, once his program is approved, issue the order.

The sources said Reagan was aware that his top aides were exploring this idea in Congress but that he had not yet signed off on such a compromise.

Reagan apparently made little headway yesterday in his efforts to win House approval of the aid package, as both sides worked feverishly to shore up their positions. The House will begin debate on the measure today with a vote expected on Thursday.

Two separate meetings were held between White House officials and key House members. In the second, smaller session, the House members were represented by Rep. Dave McCurdy (D-Okla.) and Rep. Rod D. Chandler (R-Wash.). Representing the White House were Dennis Thomas, deputy to chief of staff Donald T. Regan; deputy national security adviser Donald Fortier; and White House legislative liaison Will Ball.

Administration officials said they were concerned by indications that Democrats wanted to defeat Reagan's proposal to provide $100 million to the rebels on Thursday, and then wait for a month before voting on the compromise.

This would mean, in effect, a four-month delay in sending aid to the Nicaraguan rebels, the sources said.

The House Democrats said Reagan, during a 45-minute meeting in the Cabinet Room, repeated a litany of familiar arguments for the proposed $70 million in military assistance and $30 million in nonlethal humanitarian aid for the contras.

Several of the lawmakers said after the meeting that they remain undecided, but at least two, Reps. Marilyn Lloyd (D-Tenn.) and Albert G. Bustamante (D-Tex.), said they will vote against the administration aid package on Thursday.

Senate Majority Leader Robert J. Dole (R-Kan.) and Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.), who met with Reagan later yesterday, confirmed that the White House faces a difficult task in the Democratic-controlled House.

Dole said the administration is picking up support for the aid package, but added, "I think they're a little bit short in the House."

White House spokesman Larry Speakes, although still predicting a White House victory, said "we still have a ways to go." Speakes said the administration is 10 to 12 votes short of a majority in the House.

The personal lobbying by the president was part of the last-minute maneuvering that pitted the White House against the House Democratic leadership. House Majority Whip Thomas S. Foley (D-Wash.) insisted that there is a "conclusive" majority against the aid package and accused the administration of trying to create a false impression that Reagan was rapidly overtaking his House opponents.

Foley said he expected about 205 Democrats and between 10 and 20 Republicans to vote against the aid package.

There were also accusations that the White House was attempting to gain votes by promising favors to key lawmakers. A House Democrat opposed to the aid package said there was "some erosion" in the vote count because of administration efforts to win converts by giving them "bridges, roads or other things they need" in their districts.

"There's a lot of renting and leasing going on," he said.

A White House official acknowledged that such discussions had taken place with unnamed lawmakers, but said they had been initiated by undecided members of Congress, both Democrats and Republicans.

"This sort of thing goes on whenever there is a significant vote -- it's political reality," he said.

Asked whether issues other than Nicaragua were being discussed with undecided lawmakers, Speakes said, "Sometimes other issues are raised, and generally the president promises to look into their concerns on an issue."

As the vote neared, both sides maneuvered for a critical psychological advantage -- the appearance of inevitable victory. Thus, the group of supposedly undecided Democrats who went to the White House yesterday included one, Rep. G.V. (Sonny) Montgomery (D-Miss.), who was already committed to vote for the aid package, and others, including Reps. Ike Skelton (D-Mo.), Charles Stenholm (D-Tex.) and George (Buddy) Darden (D-Ga.), who are thought to be lined up with the administration.

But it also included Rep. Timothy J. Penny (D-Minn.), who said he was always inclined to oppose the aid package and would vote that way Thursday.

Rep. Jim Chapman (D-Tex.), who said he left the White House meeting still undecided, said Reagan's arguments for the aid package were undercut earlier yesterday when he was briefed by two officials of the Central Intelligence Agency.

Chapman said the CIA officials told him that it will be "very, very difficult" to pressure the Sandinista government of Nicaragua into peace talks and reforms -- ostensibly the objective of administration policy -- or to drive the regime out of power. "They do not believe that $100 million and 18 months the length of the aid package is going to do the job."

While attention was focused on the coming House vote, congressional leaders said it is only the first round in what is likely to be a protracted legislative battle.

Privately, even some Democrats concede that Reagan is likely to win some form of aid to the contras from Congress this year and that the battle is merely over how much compromise will be involved.

Foley said yesterday that an aid package that includes a delay in release of the funds to allow renewed diplomatic efforts toward a peaceful resolution, and a second vote by Congress if negotiations fail, would pass the House. Such a compromise may be fashioned in the Senate if the administration loses in the House, GOP strategists suggested.