The House voted 396 to 3 yesterday in favor of a resolution urging President Reagan to press for "unconditional discussions among the major political factions in El Salvador in order to guarantee a safe and stable environment for free and open democratic elections."

While the resolution might seem on the surface to advocate a significant departure from current U.S. policy, the administration did not oppose it and House Republicans insisted it did not amount to a call for negotiations with the guerrillas.

Opponents of administration policy toward El Salvador hoped the resolution would be interpreted as a slap at the administration for refusing to encourage negotiations with Salvadoran guerrillas until they lay down their arms and participate in elections set for March 28.

But Republican House members, seeking to avoid confrontation on this politically explosive issue in an election year, supported the resolution wholeheartedly, insisting that the phrase "unconditional discussions" does not mean unconditional negotiations.

The net effect of the vote was to permit both sides to claim victory. The resolution "flies in the face of the administration position," said Rep. Gerry E. Studds (D-Mass.), a sponsor. "The president has opposed unconditional discussions. This measure recognizes that unconditional discussions are necessary before the election."

However, Rep. Robert J. Lagomarsino (R-Calif.) said the intent of the resolution was to curb human-rights abuses and support free elections in El Salvador. "The general thrust of the resolution is supported by the administration," he said.

While several Republicans criticized the leftist rebels for boycotting the upcoming elections, Rep. Stephen J. Solarz (D-N.Y) argued that, in view of the alleged massacres by both sides, "it is no more realistic to expect the guerrillas to lay down their arms and participate in an election supervised by the government security forces than it would be to expect the security forces to lay down their arms for an election supervised by the guerrillas."

Liberal Democrats expect that little will be resolved by elections that are boycotted by El Salvador's leftist factions. These Democrats would halt military aid and push for immediate negotiations between the guerrillas and El Salvador's military-civilian government to bring about a peaceful solution. The administration, on the other hand, wants to increase military aid and refuse negotiations that might grant guerrillas more power than they have achieved militarily.

If yesterday's resolution was confusing to those who might try to discern a sense of direction from Congress, Majority Leader James C. Wright (D-Tex.) had a ready explanation. "We often express ourselves on a subject when we don't know what to do about it," he said.

Studds said the resolution "means different things to different people. In an election year, members welcome the opportunity to vote on things they can describe as going either way." A more critical test, he said, could come later this year when the administration is expected to send to Capitol Hill a supplemental appropriations request for $35 million in military aid and $100 million in economic aid for El Salvador.

On another Latin American issue yesterday, Sen. Edward M. Kennedy (D-Mass.) used the nomination of a new ambassador to Chile as the vehicle for a denunciation on the Senate floor of Chile's record on human rights. Kennedy said the nominee, James D. Theberge, was "insensitive" to Chile's human-rights record. Theberge's nomination was approved 83 to 12.