In a direct, bipartisan challenge to Reagan administration policies in El Salvador, a House subcommittee unanimously approved a resolution yesterday urging the president to "press for unconditional discussions" among the major factions in that war-torn country to help guarantee open elections next March.

The subcommittee action comes at a time of heightened tensions in Cuba and Nicaragua because of suspicions that some American military operations may be contemplated to counter the leftist insurgencies and their supporters in Central America. Both congressional and Pentagon sources said yesterday, however, that there were no indications that any such U.S. military action against either country was imminent.

Pentagon officials said privately that, to the contrary, what seemed more likely was "more intimidation" and stepped-up political action against Havana by other countries, possibly in the form of broader trade embargos and economic pressures, and possibly greater military assistance for other Central American countries such as Honduras.

These sources say the State Department also is pressing for more military aid to El Salvador.

Rep. Michael D. Barnes (D-Md.), chairman of the inter-American affairs subcommittee of the House Foreign Affairs Committee, said in an interview after the 9-0 vote that "it seems to me we are at a crossroads" for American policy in El Salvador.

"In general we have one of two options," Barnes said. "We can escalate...quite substantially...our military" involvement in that country "or we can seek some kind of political accommodation. And what the subcommittee just voted unanimously--and I would note that some of the most conservative Republican members of the House are on this committee--is to urge the administration to reverse its course from attempting to resolve this crisis militarily and move to a negotiated answer.

"So what's happened today is very significant," Barnes said, "and I was frankly surprised and pleased" that the four Republicans on the panel joined the five Democrats in supporting a resolution "which is clearly counter to the Reagan administration policies."

The administration and the U.S.-supported government in El Salvador have opposed a negotiated settlement with left-wing guerrilla groups or political groups linked to them.

Instead, they want the rebels to lay down their arms, renounce violence and take their fair chances in free elections. The adminstration has said that the insurgents should not be granted through negotiations "the share of power the rebels have not been able to win on the battlefield."

The United States also feels the electoral process is a way to isolate the far left groups and demonstrate popular support for the government.

But unless "a degree of understanding" is reached between factions, Rep. Gus Yatron (D-Pa.) said yesterday, the violence-free conditions for elections can't be achieved. Yatron sponsored the resolution, which was amended by Rep. Benjamin Gilman (R-N.Y.). Gilman was successful in removing some "code words" which he contended could be construed by the "far left" in El Salvador as "confirming their position" and which they could use for propaganda.

Questioned after the session, Barnes said that the subcommittee had been briefed yesterday by the CIA, Defense Intelligence Agency and the State Department on the situation in the region. He said they did not give him any feeling that new U.S. military actions were close at hand.

He added that Secretary of State Alexander M. Haig Jr. has publicly made it clear that all options are open with respect to dealing with Cuba and that there was "no doubt" that some very strong options were among them. He said a lot of committee members had been hearing from Cubans who were very concerned that a U.S. invasion was imminent.

White House spokesman David Gergen said yesterday that the administration did not consider the situation in El Salvador to be "desperate."