Secretary of State George P. Shultz is to leave today on a three-day swing through Central America for talks with area leaders at a moment of tension and hope for progress toward regional peace.

The focus of the trip is the inauguration Thursday of Nicolas Ardito-Barletta as president of Panama. Although Ardito-Barletta is Panama's first popularly elected president since 1968, his victory was tarnished by charges of massive ballot fraud.

With Colombia, Venezuela and Mexico, Panama is one of the four Contadora nations whose draft peace treaty now appears likely to offer a possible negotiated settlement of the thorny conflicts in Central America. Diplomats convening for the ceremonies expect that to be a major topic of conversation at the inauguration.

Shultz will visit President Jose Napoleon Duarte of El Salvador on the way to Panama and President Miguel de la Madrid of Mexico on the way back. He is also scheduled to stop briefly in Puerto Rico on Friday to greet Pope John Paul II before returning to Washington.

Duarte offered during a speech to the United Nations this week to meet unarmed and in person with leaders of the leftist guerrillas who have been trying to overthrow the Salvadoran government since 1979. The guerrillas, after some astonished confusion, have accepted and the meeting is scheduled to take place Monday in La Palma, a town near the Salvadoran border with Honduras, deep in territory involved in the conflict.

In a background briefing yesterday for reporters, a senior State Department official said the United States is "very comfortable" with Duarte's initiative, calling it "a natural evolution of what has been going on." He said there had been no mention of sharing power with the guerrillas, an idea the Reagan administration has opposed.

"It is the first round, and in one form or another I would say it would not be the only round," the official said. State Department spokesman Alan Romberg earlier yesterday called the initiative "far-reaching and courageous . . . a very positive development."

Romberg emphasized that although Duarte had shown the text of his speech in advance to Jeane J. Kirkpatrick, the U.S. ambassador to the U.N., "it's his proposal . . . any suggestion that is anything other than his proposal would be misplaced."

In private talks, Shultz is expected to try to explain the U.S. position demanding changes in the Contadora draft treaty, notably a strengthening of its section on verification of treaty compliance. When the leftist government of Nicaragua unexpectedly accepted the latest Contadora draft Sept. 21, U.S. diplomats were forced to go public with reservations they had previously expressed in private.

Foreign ministers involved in the Contadora process have been scheduled to meet in Panama Monday to discuss final proposals for changes in the treaty. But Honduras last week invited the five potential signers of the pact to meet Oct. 19 for more discussions.

Mexican diplomats privately have expressed irritation with the U.S. stance.

At the briefing, the senior official said there is still "a total disconnect" between the draft proposals for furthering democratic processes in Central America and Nicaragua's plans to hold its presidential election on Nov. 4