President Reagan last night attempted to rescue his embattled contra aid package on the eve of a decisive vote in the House by promising to give Congress the final say on whether additional lethal aid should be delivered to the rebels opposing the Marxist government of Nicaragua.

In a speech that the three major television networks refused to carry {Details on Page C1}, Reagan called today's vote on his request for another $36.2 million in aid for the contras "up or down for Central America . . . . win or lose for peace and freedom . . . . yes or no to America's national security."

House Majority Whip Tony Coelho (D-Calif.), responding to Reagan's offer to give Congress a role in certifying whether Nicaragua is complying with the peace process agreed to by the five Central American presidents last August, said, "The president's offer is too little, too late. It misses the point, and it won't save his package."

White House chief lobbyist Will Ball, one of the architects of Reagan's 11th-hour maneuver, said he was "optimistic it will make a difference in the House but whether enough to carry the package is not clear." Reagan agreed to give Congress the last word on lethal aid after House Republican leaders informed the White House that the package faced almost certain defeat without this provision.

But the concession came too late to change the decision of the three major networks, which had declined for the first time to carry a prime-time Reagan address, chiefly on grounds there was no news in it. All the networks carried 37 previous Reagan prime-time speeches except for one speech on the economy that ABC declined to carry in 1982.

Ninety percent of the aid package that Reagan urged Congress to pass is for "nonlethal" assistance that includes food, clothing, medicine and communications and transport equipment. The other 10 percent, $3.6 million, is for lethal aid, mostly ammunition, that will be held in escrow until March 31 and could be made available to the contras if Reagan determines that they and the Sandinista government of Nicaragua have not achieved a ceasefire.

Reagan said in his speech that he would abide by a "sense of the Congress resolution" on whether this lethal aid should be released.

Not included in the package is $20 million for insuring contra resupply planes and funds, estimated at from $3 million to $7 million, for radar-jamming equipment to protect these planes in flight.

Declaring that the "freedom fighters are an insurance policy in case the Sandinistas again go back on their word," Reagan said that the Soviets would continue to provide military assistance to the Sandinistas. If Congress rejects the package, Reagan said, "the freedom fighters may soon be gone and, with them, all effective pressure on the Sandinistas."

The speech, televised nationally only on Cable News Network, capped a day-long lobbying blitz by both sides to persuade key swing voters in the House. The president held five meetings with members of Congress and made about a dozen telephone calls, officials said.

House Democratic leaders remained confident they have the votes to block the new round of aid. A source in the Democratic leadership said that 220 lawmakers would vote against the president. That would be two more votes than the 218 needed for a majority if all 435 members vote, but would actually translate into a larger margin because of vacancies and abstentions.

House Speaker Jim Wright (D-Tex.) and Majority Leader Thomas S. Foley (D-Wash.) predicted that Reagan's speech would do little to affect the outcome even if the president made a last-minute promise to give Congress a role in triggering the release of the $3.6 million in lethal aid.

"This is a case when he is speaking for a policy that a majority of the country rejects," Foley said. "I'd be surprised if it had a substantial effect."

Others said such a concession by Reagan could sway some votes, but not enough to overcome resistance to any amount of new military aid to the rebels.

But Rep. Dante Fascell (D-Fla.), chairman of the House Foreign Affairs Committee and a supporter of contra aid, said, "It has a reasonable chance of being approved."

"It could tighten the vote up a bit," said Rep. Jim Slattery (D-Kan.), a House moderate who said he would vote against the Reagan package because of the inclusion of military aid. Slattery said he was also convinced by a pledge by the House Democratic leadership to propose an alternative funding plan that would be restricted to humanitarian aid.

"The peace process appears to be working," Slattery said. "Conservatives and moderates are reluctant this time to vote for additional military assistance. We believe there's a lot more to be done in Central America than aid the contras."

Reagan has made the contras a consistent cause for the past six years. He made nationally televised appeals for contra aid on May 9, 1984, and March 16, 1986. But the issue has never been popular with the American electorate, reaching a low point in the Washington Post-ABC News poll in January 1987, when 22 percent of those surveyed supported it.

Support for military aid to the contras peaked in July after Lt. Col. Oliver L. North's dramatic testimony before the Senate-House committees investigating the Iran-contra affair. A Washington Post-ABC News survey during the last week in July found that 41 percent supported aid to the Nicaraguan rebels, while 49 percent opposed further assistance.

A Post-ABC poll in October showed that support for contra military aid had eroded to 33 percent, while opposition had increased to 61 percent. In December, 35 percent of those questioned in a CBS-New York Times poll favored military and other aid to the contras while 53 percent opposed it.

Among those lobbying the issue on Capitol Hill was Costa Rica's ambassador to Washington, Guido Fernandez, who met with moderate Democrats to relay the opposition of his president, Oscar Arias, to any further military aid to the rebels. Arias is the author of the Central American peace plan.

Washington Post director of polling Richard Morin and staff researcher Michelle Hall contributed to this report.