Salvadoran leftist political leader Guillermo Ungo called on the United States today to participate in peace negotiations between rebel forces and the Salvadoran government.

Ungo said that while rebel negotiators expect to meet again with their Salvadoran government counterparts before the end of next month, the United States should provide "stronger backing" for the peace process.

Ungo, head of the Democratic Revolutionary Front, the civilian wing of El Salvador's guerrilla forces, also said U.S. diplomats should assume a "higher profile" and state support for President Jose Napoleon Duarte's commitment to a dialogue with the guerrillas. The rebel side frequently tried in the past to engage Washington, rather than San Salvador, in talks.

Direct contacts between U.S. and Salvadoran rebel negotiators could be arranged as a process parallel to the left's talks with the Salvadoran government, Ungo suggested.

"We consider the United States to be a party to the El Salvadoran conflict," said Hector Oqueli, a rebel spokesman with Ungo at a press conference here.

The U.S. special ambassador for Central America, Harry Shlaudeman, has not responded to rebel requests that he meet with Salvadoran opposition representatives, possibly "in a separate arena or at a different table," Ungo said. Shlaudeman has held occasional talks with the Sandinista government of Nicaragua.

Business groups and others "of the right" are pressuring Duarte to suspend the talks, Ungo said, adding that "there are sectors within the Army who favor the dialogue, but who are now on the defensive."

A partial Christmas season truce discussed at the last talks will not be respected by guerrillas if they are attacked and obligated to undertake "defensive actions," Ungo said. Rebel leaders offered a holiday cease-fire after rejecting "unacceptable" government conditions for a formal Christmas truce, he said.

Government negotiators demanded that the guerrillas cease all supply operations and suspend propaganda broadcasts, the rebel spokesman said.

Washington Post correspondent Robert J. McCartney added from San Salvador:

U.S. Ambassador to El Salvador Thomas Pickering predicted that the government would respect the informal holiday halts in hostilities as outlined by the guerrillas.

Pickering also said the United States supports Duarte "without reservations" in the dialogue with the rebels.