President Reagan, seeking to save his bid for $100 million in aid to the Nicaraguan rebels from a defeat in the House, told Congress yesterday that he would restrict the use of the money for the first 90 days to defensive weapons, logistics and training, while continuing to seek a negotiated settlement there.

White House officials said the 11th-hour offer had given the president enough support in the House to assure a "very, very close vote," but several key Democratic swing voters rejected the proposal and House Democratic leaders predicted Reagan would get a "rude awakening" on the House floor today.

The rival claims of strength set the stage for an emotional showdown this afternoon on what may be the most significant foreign policy vote in Congress during this election year.

House Democratic vote-counters said at the end of the day they were still about a dozen votes ahead, while the White House claimed the president was within three votes of the 218 needed to win.

Yesterday's maneuvering capped nearly 30 hours of negotiations on Capitol Hill and at the White House and was carried out as the House began formal debate on Reagan's request for $70 million in military aid and $30 million in nonlethal assistance. The issue is framed as an all-or-nothing proposition.

The last-minute scrambling, designed to give critical swing voters some maneuvering room, opened the door to the possibility of additional votes later on the issue and suggested that some type of aid would be approved for the Nicaraguan contras, even if Reagan loses today in the House.

The House Democrats who rejected Reagan's new offer did so with assurances from House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) that if the $100 million aid package is voted down today, the House would consider alternatives April 15.

O'Neill's assurance was designed to win support from House members who favor some kind of assistance to the contras but are reluctant to back the president's request as written.

The White House offer came in response to criticism from congressional moderates in both parties, who said they were reluctant to grant military aid without assurances that diplomatic efforts would be made first.

Backing away from its earlier insistence on a straight up-or-down vote on Reagan's plan as originally proposed, the White House announced that it would send a presidential message to Congress saying that if the measure is approved, Reagan will issue an executive order setting terms for use of the funds.

White House spokesman Larry Speakes said those terms would permit $25 million to be used within 90 days for purchase of air defense missiles, logistics and communications and intelligence operations.

It would also pledge $2 million to the four-nation Contadora regional peace group, but additional funds could be spent only after a report from a five-member presidentially appointed commission that satisfactory efforts had been made to achieve a diplomatic agreement. The commission's role would be purely advisory.

To launch those efforts, Speakes said, Reagan would immediately dispatch his special envoy, Philip C. Habib, to the Contadora nations to begin such discussion and to pressure the leftist Sandinista government to begin a "national dialogue" with the contras.

After that commission reported, Congress would have 15 days to vote to block expenditure of the remaining funds.

Among the Democrats who rejected Reagan's offer were Reps. Dave McCurdy of Oklahoma, Jim Chapman of Texas and Marilyn Lloyd of Tennessee.

McCurdy played a key role in fashioning an agreement last year for $27 million in nonlethal aid after the House had rejected a request for military assistance. But yesterday, he said an executive order did not provide enough assurance that the president would restrict military assistance until diplomatic efforts were exhausted.

Lloyd said she would have preferred that no military assistance be permitted until diplomatic efforts had been tried.

Rep. Rod D. Chandler (R-Wash.), a key GOP swing voter, said the Reagan offer had given the president the support of about seven or eight previously uncommitted Republicans. "It will be close, but I think this will put him over," Chandler said.

House Minority Leader Robert H. Michel (R-Ill.) continued his criticism of White House compromise talk as counterproductive to his efforts to to line up votes for passage of the up-or-down measure.

At one point during a lengthy meeting with reporters, however, Michel said, "If there is something out there that's that magic thing that gives me the assurances [of passage] I can't dismiss that thing out of hand."

McCurdy is only one potential sponsor of a compromise. Another plan, likely to offer no assistance to the contras, is expected to come from Rep. Lee H. Hamilton (D-Ind.), chairman of the House Permanent Select Committee on Intelligence. Rep. James C. Slattery (D-Kan.) has also talked of a possible compromise that would involve humanitarian aid.

House Majority Leader James C. Wright Jr. (D-Tex.) said yesterday that any measure approved in April is likely to be attached to a supplemental budget appropriation for the current fiscal year.

The Reagan request for $100 million also must be considered in the Senate, where observers say it could coast to victory if approved in the House or be resurrected in compromise form if rejected today.

Yesterday's maneuvering took place as Habib, Secretary of State George P. Shultz and Assistant Secretary of State Elliott Abrams met with House members in a room near Michel's office. Two contra leaders received visitors in the office of House Assistant Minority Leader Trent Lott (R-Miss.), and congressional supporters of the aid package put large aerial photographs of Nicaraguan prisons and captured weapons in the Speaker's Lobby just off the House floor.