The House, striking what could be a mortal blow against the centerpiece of the Reagan administration's Central American policy, last night narrowly rejected the president's request to provide $36.2 million in new aid to the rebels fighting Nicaragua's Marxist government.

The 219-to-211 vote killing President Reagan's aid package to the contras came at the end of a divisive 12-hour debate and a furious lobbying campaign in recent weeks that included an 11th-hour concession to Congress by the president. At the end, 207 of the Houses' 257 Democrats and 12 of its 177 Republicans voted against the president's proposal.

Defeat of the package, which included $3.6 million in lethal assistance, means that for the remainder of Reagan's term the White House will not be guaranteed another congressional vote on the issue that has dominated its Central American agenda. However, the administration still can seek additional aid through the regular appropriations process -- a route that is more easily blocked by the Democratic controlled Congress, but one that the White House will almost certainly try.

However, the House leadership has said it will propose a package of purely humanitarian assistance for the contras so they will not be totally abandoned. White House spokesman Marlin Fitzwater called it "little more than a refugee plan." But another White House official said the president will "do whatever he can" to help that package, even though he considers it "woefully insufficient."

After the vote, Fitzwater said, "We are disappointed that the House of Representatives did not vote to keep pressure on the Sandinistas during the peace process. We thank our many supporters in Congress who worked so hard on behalf of this issue. We will continue consultations with these congressional supporters and others concerning the future of the resistance and the peace process."

In killing the president's request, the House rejected Reagan's arguments that the contras are the United States' best bulwark against communist expansion in Central America and that continued financial support is necessary to make the Sandinista government adhere to the Central American peace process that began last summer.

Instead, the House accepted the views of the Democratic leadership that a new round of aid would upset the delicate process of achieving peace in the region by encouraging Nicaraguan President Daniel Ortega to abandon his commitment to democratization and the recently begun cease-fire talks with the contras.

The closeness of last night's vote reflected the high political stakes of an election year, the delicate stage of the six-month-old Central American peace process and the deep divisions caused by the most contentious foreign policy issue of the Reagan presidency.

Both sides billed the vote as a showdown that could end the administration's seven-year effort to topple Nicaragua's government by supporting and arming the contras -- a policy that Congress has backed with more than $200 million in direct aid.

Rep. Mickey Edwards (R-Okla.), who led the floor fight for the package, called it "a very serious defeat" for the president's policy in Central America, one that would be very difficult to reverse.

House Speaker Jim Wright (D-Tex.) said last night's vote effectively ends military aid for the contras unless "the government of Nicaragua were to misbehave amd renege on its commitments. . . . That would change the situation."

{There was no immediate reaction from Nicaragua's president, but its U.S. ambassador, Carlos Tunnerman, said in interview on Nicaraguan radio that the vote was a "triumph." He warned, however, that "as long as the Reagan administration exists," Nicaragua is not out of danger, Washington Post correspondent Julia Preston reported from Managua.}

{Contra spokesman Bosco Matamoros criticized the Democratic Party and vowed that the rebels would keep fighting despite the defeat, Post correspondent William Branigan reported.}

Even though the closely divided House has previously fought over contra aid, yesterday's day-long debate was laced with impassioned rhetoric on both sides.

The House began debating Reagan's request at 10:30 a.m., 14 hours after the president broadcast an appeal for his package that included an inducement designed to sway some of the few undecided members. In agreeing shortly before his speech to give Congress a final chance to block lethal aid, Reagan bowed to pressure from House Republican leaders and former Virginia governor Charles Robb, a Democrat, who argued the concession was necessary to give the package a chance.

Of the $32.6 million of nonlethal aid in Reagan's $36.2 million request, $7.2 million would be for humanitarian aid in the form of food, medicine, shelter and clothing. The balance would be "non-lethal" aid that could include items that could be used in fighting such as jeeps, helicopters and spare parts.

In addition to the $36.2 million, the package also proposed to make available from previous defense appropriations $20 million to cover the cost of replacing lost aircraft and several million more for passive air defense equipment.

The lethal aid in the president's initial proposal would be held in escrow during March and released if the president certified that no cease-fire is in place in Nicaragua and that a lack of good faith on the part of the Sandinista government was the reason.

In his speech Tuesday, however, Reagan offered to give Congress a role in triggering the release of the lethal aid. He said he would withhold the lethal aid if Congress adopts a resolution stating that the Nicaraguan government is in compliance with the peace process within 10 days after the president authorized release of the money.

House Democratic leaders greeted that offer scornfully yesterday, saying that any such resolution could be filibustered beyond the 10-day period in the Senate, effectively eliminating Congress' ability to block the military aid.

Yesterday's debate capped an extraordinary lobbying campaign by both supporters and opponents of continued aid to the contras.

Reagan talked by telephone or face-to-face with 10 House members. Leading members of his Cabinet and staff also telephoned potential swing voters.

The vote came against the backdrop of last year's revelations that the administration had ignored an earlier congressional cutoff of aid and continued a covert program of supplying arms to the contras. It also came after six months of progress toward implementation of a regional peace agreement that was signed by the five Central American presidents on Aug. 7. That accord has led to cease-fire talks between the Sandinistas and contras and to recent democratization efforts by Managua, including the lifting of its state of emergency.

Staff writer Lou Cannon contributed to this report.