The Contadora group opened a three-day meeting in Panama today amid predictions that it would fail to meet its own deadline to arrange a regional peace treaty for Central America by the end of the conference.

Nicaragua effectively scotched hopes for reaching an accord anytime soon when it announced on Nov. 11 that it would sign a Contadora pact only if the United States pledges to halt its "aggressive policy" toward Managua's Sandinista government. Washington has indicated no intention of making such a promise.

"Contadora is now on a life support system, and everybody is just waiting for someone to pull the plug," a senior West European diplomat, who follows Contadora, said.

In a similar vein, Costa Rican Deputy Foreign Minister Gerardo Trejos was quoted as saying that Nicaragua's stance left Contadora "at the point of death."

But senior officials of several countries attending the conference predicted that the group would continue its work, mainly because it was unwilling to admit failure.

A proposal was to be made seeking to narrow differences over verification of proposed accords on military maneuvers and arms reductions, but agreement was not expected this week, according to Latin diplomatic sources.

"There's a certain amount of discouragement at the moment . . . but there is no alternative except to continue," a Honduran official said.

The Contadora group has been striving for nearly three years to put together a regionwide peace treaty for Central America. The group is made up of four countries -- Mexico, Venezuela, Colombia and Panama -- and is named for the tiny Panamanian island where it first met.

The other five countries at the conference are the Central American nations that actually are attempting to reach the agreement: Nicaragua, Honduras, El Salvador, Costa Rica and Guatemala.

The basic division among the five Central American countries has been between Nicaragua's leftist government, on one side, and its three neighbors Honduras, El Salvador and Costa Rica, on the other.

The latter three also are U.S. allies and aid recipients. Guatemala has taken the position that it will accept whatever the others can agree on. It does not border on Nicaragua, and has received minimal amounts of U.S. military aid because of congressional concern over human rights violations by its armed forces.

In an effort to stop months of squabbling and reach a conclusion, the nine countries promised on Oct. 7 to agree on a peace treaty within 45 days. That deadline expires Thursday, but Mexican, Nicaraguan, Honduran and other officials said the group almost certainly would need more time.

In a potentially major shift in bargaining positions, Nicaragua apparently has become the major "spoiler" in the Contadora talks.

In September 1984, the Sandinista government embarrassed the United States by declaring publicly that it was willing to sign a Contadora draft treaty that Washington and eventually its Central American allies did not like.

Now, after several changes in the draft that seem to reflect relatively moderate concessions to its neighbors, Nicaragua has said it will not endorse the pact until the United States stops supporting the Nicaraguan antigovernment guerrillas known as contras.

Nicaragua's principal objections to the latest draft treaty concern U.S. military maneuvers in the region and measures to stop the arms race there.

The Sandinistas want an "absolute prohibition" on foreign military maneuvers in Central America.

This is aimed at preventing the United States from continuing its maneuvers in Honduras, which have had the admitted purpose of intimidating the Sandinistas next door.

The current draft allows such maneuvers to continue for an unspecified time, although it fixes certain limitations on them. Advance notification must be given, for example, and maneuvers are not permitted to take place within 50 kilometers, or 31 miles, of an international boundary.

The September 1984 draft called for all foreign military maneuvers to end in the region within 30 days.

In addition, Nicaragua argues that the current draft would force it to cut back its arms levels at a time when it needs weapons to battle the contras.

But the criteria in the proposal for judging Nicaragua's arms requirements are virtually identical to those contained in the draft last year that the Sandinistas accepted.

The current draft, like the one last year, would force Honduras, Costa Rica and El Salvador to shut down contra camps and other facilities in their territory.

Some diplomatic observers suggested that the Nicaraguans doubted there would be such a crackdown as long as Washington was supporting the rebels.