IS THAT a fleck of light at the end of the tunnel in El Salvador? Through the Costa Ricans, a line has been opened between Salvador's appointed president and the leader of the guerrillas' political allies. The Salvadoran government, having put on paper a "pact" signed by the parties that fought parliamentary elections last March, now speaks of a "peace commission" to develop "a practical amnesty and disarmament program (covering the guerrillas), probably in conjunction with some form of security guarantees to persuade the political parties who refused to run candidates for election in March to join in the electoral process." Guerrilla groups hint they may drop some of the demands the government found unacceptable in the past.

The picture is one of hesitation, skepticism and resistance at both extremes. But there is also a sense of possible movement toward consensus that has not existed since reform-minded officers overthrew the old feudal apparatus in 1979 and the revolutionaries, thus preempted, moved to civil war.

The government's reform and military programs, flawed as they are, may have something to do with these tentative stirrings. Their principal source, however, appears to be the elections last March. These strengthened politics as the arena in which the masses of Salvadorans plainly wish to work out their country's destiny. This, in turn, gave a better purchase to those within the Salvadoran political system who doubt that the country can endure a military struggle to the end and who wish to try to split the left and draw in those parts of it open to political competition. The same strengthening of political tendencies may have touched the left. At the least, the high popular participation in the elections, despite a fierce guerrilla campaign to spoil the poll, undercut any guerrilla argument that the masses could be won over or intimidated by armed struggle.

If the elections and their delayed aftermath are the key elements, it cannot be irrelevant that the signals coming from Washington changed subtly over the summer. The United States continues to insist, with the Salvadoran government, that it will not support a negotiation leading to guerrilla participation in the government, though it will support talks leading to the left's participation in the electoral process. Nonetheless, the tone of policy is different. Under former secretary of state Alexander Haig, it was one of confrontation in the name of anti-communism and under Secretary of State Shultz, it has shifted more toward local and regional conciliation. Not much attention has been given to this shading in Washington. In Central America, where the stakes are much higher, it has been widely noted.

Central America is too torn and polarized to permit any easy optimism. Nor are the present hints of change equally acceptable in all quarters. The Salvadoran feudal right, for instance, like the extreme right in the United States, professes to see an ominous softening of Ronald Reagan's policy. We see something else, especially in El Salvador: a continuity with the latter-day Carter policy that makes it possible for the mainstream in the United States to support a policy of firmness and reform. In brief, though El Salvador still is engaged in a desperate struggle, it is becoming possible to ask whether the Reagan policy may not work.