The Salvadoran guerrilla command, after weeks of hesitation and ambiguity, assumed responsibility today for the kidnaping of President Jose Napoleon Duarte's daughter and declared that the abduction could help lead to his downfall.

The rebels' acknowledgment, on their Radio Venceremos, came as Roman Catholic Church intermediaries tried to shore up a shaky deal for her release after six weeks of captivity in exchange for 22 rebels held prisoner by the government.

This bargain, reportedly all but sealed late last week, has threatened at the last minute to fall apart, leading to an additional delay of at least several days, church negotiators and government officials said.

The rebel declaration apparently signaled the end of a debate in guerrilla ranks over how to portray the kidnaping, which has been criticized widely in El Salvador and abroad but which nevertheless has brought at least temporary political advantages to the guerrilla alliance, the Farabundo Marti National Liberation Front, FMLN by its Spanish initials.

Hammering on reports of dissatisfaction among Army officers unhappy with Duarte's conduct in negotiations for his daughter's release, the broadcast also mentioned grumbling in his Christian Democratic Party.

These tensions, particularly in the officer corps, could lead to Duarte's ovethrow, the broadcast said.

Salvadoran analysts, including an informant sympathetic to the rebel cause, also indicated resentment among some officers. But the military as a whole remains loyal to the president, indicating that this seeming benefit to the rebels is likely to be short-term, these sources and a foreign military source said.

"Nationally and internationally it is recognized that the operations of the capture of the Christian Democratic functionary and the attack on and seizure of the Salvadoran Armed Forces Military Training Center were triggers, intelligent operations of the Farabundo Marti National Liberation Front that have hastened to a question of hours the collapse of the dreams of Duarte grandeur," said the announcement today.

The radio referred repeatedly to Duarte's daughter as a "functionary," alluding to her role as publicity director in his election campaign last year and her management of a San Salvador radio station sympathetic to his Christian Democratic government. The other operation cited was an Oct. 10 attack on the main Army training base at La Union, in which 42 Salvadoran soldiers were reported killed and twice that many injured.

Communications and Culture Minister Julio Rey Prendes, Duarte's spokesman in matters regarding the abduction, has long insisted that the government was dealing with the FMLN in its efforts to free the president's daughter, Ines Guadalupe Duarte Duran, 35, and a 23-year-old friend kidnaped with her, Ana Cecilia Villeda. The abductors have identified themselves only as the Pedro Pablo Castillo Front, whose existence was announced last July by the FMLN.

A Salvadoran source with close ties to the rebel movement said the kidnaping apparently was carried out by a group composed mostly of members of the Salvadoran Communist Party's military wing, the Armed Forces of Liberation, one of the FMLN's five allied armies. The overall FMLN command took over responsibility for negotiating a prisoner swap only afterward, the informant said.

It remains unclear whether those acting as the Pedro Pablo Castillo Front carried out the Sept. 10 kidnaping on their own or under orders from Shafiq Handal, commander of the Armed Forces of Liberation and a key member of the FMLN General Command, the source said. But he noted that one of the prisoners whose release has been demanded is Americo Mauro Araujo, a top-level Handal aide who was captured in August.

The informant, who is closely involved in the negotiations, said that in any case the FMLN command's earlier insistence that it was only acting as an intermediary with the abductors was part of the problem in securing an agreement. A deal struck last week with the FMLN command, he said, was to be relayed to the abductors with orders for them to notify the government by radio of their acceptance.

The message that arrived was negative and, government and church sources said, contacts resumed over the weekend on the issues still in dispute. Msgr. Gregorio Rosa Chavez, San Salvador's auxiliary bishop, said yesterday that the efforts nevertheless remain "on the right path."

The FMLN acknowledgment today also seemed designed to include the rebels' political wing, the Revolutionary Democratic Front, which has maintained steadfastly that it had nothing to do with the kidnaping and knew nothing about it.

"The unity and consolidation of the Farabundo Marti National Liberation Front-Revolutionary Democratic Front has guaranteed the realization of the people's victories," the anouncement said.

The Revolutionary Democratic Front's two top leaders, Ruben Zamora in Managua and Guillermo Ungo in Panama, were unavailable for comment on the rebel statement. They have been refusing comment on the kidnaping regularly, saying their group will define its position after negotiations end.