Reagan administration officials, while publicly opposing negotiations that would give El Salvador's leftist guerrillas a share of governmental power, are moving quietly toward talks with the insurgents aimed at inducing them to stop fighting and take part in planned elections, informed sources said yesterday.

The effort, still being planned, reportedly differs from past U.S. approaches couched in bellicose rhetoric about not permitting the guerrillas "to shoot their way into power" and focusing exclusively on calls for them to lay down their arms.

Now, the administration, working secretly through various diplomatic contacts, is said to be trying for a more broadly based agenda that would satisfy some of the leftists' demands and concerns, permit U.S. mediation between government and insurgents and lead ultimately to at least part of the left joining the electoral process.

Reports of the effort come as the administration prepares to certify to Congress that progress has been made in El Salvador toward guaranteeing human rights and reaching a political settlement, a requirement imposed as a condition for approving further military aid.

For that reason, and because of extreme secrecy surrounding the situation, it was not immediately clear whether administration officials believe the move has a real chance of success or is essentially a tactic to pacify congressional critics.

Suggestions of any move toward power-sharing negotiations have been disavowed strongly by President Reagan and key policy-makers such as national security affairs adviser William P. Clark. However, the sources said, the current effort has been approved by top officials formerly in conflict.

At a news conference yesterday, Secretary of State George P. Shultz hinted at the administration's direction in noting that the peace commission established by the U.S.-backed Salvadoran government "has stated its willingness to discuss with the left the conditions under which they might enter the political process."

Shultz added that if the United States can "facilitate that" through the efforts of special envoy Richard Stone, "we're happy to do that."

Shultz's remarks were the first official indication that the administration may be moving toward the "direct dialogue" called for by guerrilla representatives while Stone was touring Central America two weeks ago.

Ruben Zamora, North American spokesman for the guerrillas' Farabundo Marti National Liberation Front and the Democratic Revolutionary Front (FMLN/FDR), told The Washington Post yesterday that his group "is getting indications" from sources outside the U.S. government that a meeting will be held with Stone.

U.S. officials confirmed privately that Stone has a tentative go-ahead for such a meeting. They stressed that its mechanics are evolving and that the effort is being kept secret to avoid possible criticism about acquiescence in a power-sharing arrangement.

Stone, asked by The Post about his role, said: "This is a most delicate situation in which no possible participants should be saying anything at all, and therefore I won't."

The sources said Stone, in a private report to Reagan Monday on his trip, stressed that a "Latinization" process, giving greater weight to views of the region's governments, should become U.S. policy. Many of these governments have advocated greater U.S. flexibility in promoting dialogue between the Salvadoran regime and its adversaries.

Stone also has strongly endorsed the regional peace initiative of the so-called Contadora group--Colombia, Venezuela, Mexico and Panama--that wants foreign troops out of the area and is trying to mediate. Although he would not discuss his role in the negotiations, Stone said yesterday that the participants' unique approach gives them a chance of success.

"They have a cultural understanding of each other that no one else has, and so they're structuring the agenda in a very Latin way," he said. The formal Contadora agenda includes "philosophical themes on which they all agree," Stone continued, but "in their lunches and their leisure time, they're tackling real issues."

This, Stone said, was "a method U.S. diplomats could never cook up."

The U.S. task, he added, is to support the process without interference that prevents a solution from being solely Latin.

"We do much better to stand behind them and the process than we could by getting more directly involved," he said.