The Salvadoran constituent assembly canceled for the second day in a row a session intended to name the country's new provisional president, indicating that rightists have raised the stakes in the political poker game here and are trying to call what they say is a bluff by the armed forces and the United States.

After a raucous audience had waited nearly two hours, assembly president Roberto D'Aubuisson announced that the session was canceled for lack of a quorum. "It means there's no agreement yet; what else could it mean?" said an exasperated U.S. official as everyone filed out of the assembly building.

D'Aubuisson's far right Nationalist Republican Alliance party (ARENA from its Spanish initials) is using the crowbar of nationalism to try to pry apart a fragile alliance on the presidential issue between the relatively moderate Christian Democrats and the National Conciliation Party, which governed the country for 20 years for the landed oligarchy.

The State Department and the armed forces thought last week that they had convinced a majority of the 60 deputies to elect moderate banker Alvaro Magana, 56, as provisional president. They did so by suggesting that El Salvador would risk losing U.S. economic and military aid if he were not elected and that it might risk a military coup.

But ARENA officials are telling National Conciliation's 14 deputies that the Army will not move against a duly elected rightist government and that the United States will not withdraw aid from a strongly anticommunist government. They are pushing to use the combined rightist majority in the assembly to elect one of their own number.

Politicians on both sides of the argument say National Conciliation deputies are deeply split. They are the power brokers in the assembly and know that the crucial next play is theirs. Deputies normally willing to talk with reporters today refused to do so.

"The United States will have to respect the will of the people," an ARENA official said. He said the March 28 election that gave four rightist parties 60 percent of the valid votes was a mandate to oust the Christian Democrats from power they currently share with the military, and that the American public would force Congress--in voting on aid--to observe the verdict of the elections.

"The Army will never move, either. They put too much into those elections," he said. ARENA also apparently believes that while the high military command might support Magana, lower level officers do not and would resist any order to close down the assembly and take over the government.

The guerrillas, meanwhile, appear to have escalated the war in the countryside, offering strong resistance to a new military offensive in eastern Morazan Province. The rebels also overran the town of Los Perez in northern Chalatenango Province, while military patrols were reported sweeping western Santa Ana Province in search of guerrillas who previously have not been much in evidence there.