SAN SALVADOR, OCT. 3 -- Despite a day of political and logistical setbacks, President Jose Napoleon Duarte and leftist rebels prepared under tight security for a third round of peace talks to end El Salvador's eight-year-old civil war.

As of this afternoon, none of the rebel leaders scheduled to take part in the talks had arrived in the Salvadoran capital where the meeting between eight-member delegations from each side were scheduled to begin at the papal nunciature at 9 a.m. Sunday under the mediation of Archbishop Arturo Rivera y Damas.

Rebel leader Nidia Diaz, in a telephone call to a radio station, charged that the military was not allowing rebel commanders down from the hills to attend the talks.

{In Washington, rebel spokesman Francisco Altschul said government forces have surrounded the town of San Fernando, where two members of the rebel delegation had gathered, and stationed troops along the road to San Salvador, in violation of an agreement reached by both sides on arrangements for the talks.

{Reuter quoted Army operations chief Mauricio Vargas as saying, "There are units in the area that we will not withdraw. Instead, we will allow for a safe corridor." A similar dispute in September of last year prompted the guerrillas to cancel talks with Duarte in Sesori.}

The other six rebel leaders were delayed in Panama by last-minute disagreements over protocol and by bad weather, according to Guillermo Ungo, leader of the political wing of the rebel alliance, who spoke by telephone from Panama.

Tonight, thousands of people rallied here to support the peace talks. Traffic was shut off for blocks around the meeting site and roadblocks were manned along the three main highways leading to the city to check identification papers. n various embassies during the talks.

While the meetings were scheduled for only one day, the government delegation led by Duarte and the rebel side headed by Commander Leonel Gonzalez have said they are willing to extend the talks if progress is made.