President Reagan's policy initiative on Nicaragua is essentially a plan to make peace with Congress, not with Nicaragua.

It would give the antigovernment rebels in Nicaragua the right, after 60 days of talking with the Sandinista government, to choose whether to continue talking while their $14 million in U.S. aid dwindles, or take what by then would be left of the money in guns.

Their incentive to make concessions would be minimal.

In effect, the plan gives Nicaragua 60 days to agree to the demands of the rebels and Reagan before U.S. funding for the rebels' war resumes with full congressional backing. Nicaragua, and most Democrats, rejected the proposal yesterday for that reason.

But the plan alters the political landscape of the debate by allowing Congress to vote, at least initially, nonlethal funding for the rebels, who are known as "contras." This would affirm the members' distaste for blood and for the Sandinistas, and also offer them a chance to look tough.

The proposal marks the second time this spring that Reagan has converted lethal weapons into bargaining chips. He got his way in Congress on the MX missile, and he hopes to make the $14 million contra aid a bargaining chip to hold over the Sandinistas' heads. This is just the alternative that many members of Congress have urged the president to find.

Some members were at least cautiously impressed, as Reagan had hoped.

Sen. David F. Durenberger (R-Minn.), chairman of the Senate Select Committee on Intelligence, whose decision to oppose funding the rebels through the Central Intelligence Agency influenced several colleagues, said the initiative is "a positive step" that he will endorse if the eventual conversion to lethal military aid is eliminated.

But, he added, the plan "is not Reagan's Central America policy, not his Nicaragua policy; it's just a way to get rid of a bad policy the Congress wrote."

Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.), one of those who had told Reagan that his old approach to Nicaragua would never fly in Congress, said that "many who were polarized by the old formula will be willing to step back and reexamine" the new one.

The latter's prospects in Congress could be improved, Lugar said, but he stopped short of predicting victory.

Visiting Colombian President Belisario Betancur also was cautiously impressed, calling the plan "a positive step" that he would offer to the Contadora regional peace negotiations next week for possible inclusion in the group's agenda.

It is too early to predict anyone's reaction, Betancur said.

Democrats predicted defeat for the idea in Congress.

They were so unimpressed by the initiative that House leaders asked intelligence committee Chairman Lee H. Hamilton (D-Ind.) and western hemisphere affairs subcommittee Chairman Michael D. Barnes (D-Md.) to devise an alternative. Barnes said that he hopes for a bipartisan approach because "there are a lot of Republicans here who are also very concerned about the president's policy."

Barnes added that Reagan's proposed "humanitarian assistance" of food, medicine and clothing for the rebels "is really logistical supplies for an army."

Barnes said that national security affairs adviser Robert C. McFarlane, who briefed congressional leaders yesterday, "was told by both Republicans and Democrats that people will regard this as a subterfuge for getting the money."

Reagan did not help his case when he made clear that he will somehow continue to aid the rebels, even if Congress refuses.

"We are not going to quit and walk away from them, no matter what happens," Reagan said.

A senior administration official argued that Nicaragua has only to make some concessions to keep the talks going and the fighting halted indefinitely.

"The president will not allow the contras to walk away from the table," the official said. "This is the first time the Sandinistas can be sure that their actions will determine whether there is funding or not" for the rebels.

But Nicaraguan ambassador Carlos Tunnermann said in an interview yesterday that the agenda for the talks does not encourage him.

Tunnermann noted that Reagan's entire plan is based on one offered March 1 in Costa Rica by former Sandinista ambassador Arturo Cruz, exiled Nicaraguan businessmen and political leaders of the largest armed opposition group, the Nicaraguan Democratic Force.

Rejected at the time by Nicaragua, the San Jose proposal demands that the Sandinistas, the Nicaraguan state and the Nicaraguan army, now virtually synonymous, be separated.

The plan also calls for government decentralization, expulsion of foreign military personnel, an end to censorship and the state of emergency, and a cease-fire while the conference of Roman Catholic bishops and other Central American nations organize peace talks.

The agenda for the talks under this plan includes dismantling neighborhood "defense centers," dissolving the national assembly, restructuring the electoral system, organizing new elections, and a plebiscite on how to choose a new president.

In its only real concession to the Sandinistas, the proposal would allow President Daniel Ortega to remain in office while all this is done.

Tunnermann said this agenda proves that Reagan would define progress in the talks as progress toward invalidating the election of last Nov. 4, which kept the Sandinistas in power.

"This is a threat against our government," Tunnermann said. "It is only a maneuver to impress the Congress and get them to provide the $14 million."