The Salvadoran rebel alliance said today that it intended to participate in planned peace talks with President Jose Napoleon Duarte on Monday despite Duarte's rejection of several of the insurgents' proposals on how to set up the negotiations.

Rebel civilian leaders complained that Duarte's government was dragging its feet on arranging the talks, and the two sides apparently have not even begun to bargain over procedural issues. But the insurgent officials' comments indicated that they were willing to yield to Duarte's proposals and thus go ahead with the first top-level peace talks in five years of civil war.

In a separate development, new details emerged regarding the U.S. government's initial reaction to Duarte's surprise proposal on Monday to hold the talks.

Salvadoran officials said yesterday that the U.S. Embassy had warned Duarte last weekend that the initiative might be too risky, but they refused to identify the U.S. concerns. Today, informed sources said that both Duarte and the United States had agreed that the principal risk was a domestic backlash by El Salvador's powerful political right.

Since Duarte made his proposal, the United States has supported it enthusastically. While U.S. diplomats would not comment for the record on their "private communications" with Duarte, they noted that the conservative response has been subdued.

In an apparent softening of the rebels' position, rebel civilian leader Ruben Zamora said in a telephone interview that the left would send representatives to the talks even if members of the Salvadoran Armed Forces' High Command did not come with Duarte to the negotiations. The rebel statement Tuesday that accepted Duarte's invitation to the talks had demanded that members of the High Command participate.

"In no way is that a precondition. He can't impose on us who will participate on our side, and we can't impose on him who participates on his," Zamora, a member of the rebel alliance's political-diplomatic commission, said. "It's been our policy to negotiate for three years. We see it as an important step for us."

One potential snag was that Zamora, as a civilian leader, might have a more flexible view regarding the negotiations than the rebels' military leaders. One of the guerrillas' two clandestine radio stations, which are believed to reflect the views of rebel military leaders, referred today to the planned meeting with "Duarte and the members of the High Command" and thus implied that the insurgents still expected senior Salvadoran officers to be present.

Zamora also said that the two rebel military leaders to participate in the talks would be commanders of two of the five guerrilla armies that are battling the U.S.-backed government. The mere appearance of these commanders in such a forum would be a significant event, since they seldom have given interviews to the press or have even been seen by persons other than their supporters.

Zamora and Guillermo Ungo, the highest ranking civilian leader in the insurgent alliance, also said in telephone interviews that they accepted Duarte's proposal yesterday that El Salvador's Roman Catholic Church serve as the intermediary for setting up the negotiations. Both Zamora and Ungo were contacted at Ungo's home in Panama, where he lives in exile.

The church thus would act as go-between in talks on such matters as how to handle the expected large crowd of journalists and spectators, whether civilian rebel leaders would be allowed to fly into the country for the negotiations, and what building would be the site of the parley in the northern Salvadoran town of La Palma.

But confusion in the past three days over who would serve as the go-between apparently has delayed discussions on these procedural matters, with the guerrillas saying they were waiting for the church to contact them while the ranking church official here said he was waiting for the rebels to announce publicly that they accepted the church as intermediary.