The Christian Democratic Party's legislative leader charged today that efforts by El Salvador's right-wing leaders to modify the land reform program "will close the door on peaceful land redistribution."

Julio Adolfo Rey Prendes, party leader in the constituent assembly, said at a news conference that land reform provisions in the draft constitution now being considered would also "buttress the arguments of leftist guerrillas who contend violence is the only way to bring social and economic justice to El Salvador."

His denunciation climaxed a week of often stormy debate in which the Christian Democrats tried to change the way the draft constitution deals with land reform. The effort has failed so far, Rey Prendes said, because of steadfast resistance by the extreme rightist National Republican Alliance of former Army major Roberto D'Aubuisson and unwillingness by key swing vote parties to oppose D'Aubuisson.

"This means there will never be agrarian reform in El Salvador," said Jose Antonio Morales Erlich, the party's deputy chairman. He predicted that if the constitution stands as written the outcome will be more "social upheaval" and "peasant frustration" of the kind that helped generate the 3 1/2-year-old civil war here.

The outcry appeared designed at least in part to generate public concern in Washington that could be translated into arm-twisting by the U.S. Embassy here to persuade the smaller swing parties to side with the Christian Democrats in the 60-member assembly, building a majority against the rightists.

The U.S. Congress has insisted on land reform as a way to undercut leftist promises of social and economic change. It has said redistribution of large farms must be a condition for continued military aid appropriations. U.S. diplomats played a role in turning back a rightist attempt in March 1982 to legislate loopholes--similar to those in the draft constitution--into the land reform laws that are now in effect.

Rey Prendes and Morales Erlich warned that D'Aubuisson's followers on a special commission that drafted the new constitution for approval by the assembly are trying to "exploit" the document to get in the loopholes they failed to pass then.

The two party leaders said articles 104 and 105 in the draft constitution grant owners of large farms the right to sell their land before it can be redistributed to peasants. This means in effect that landowners can escape redistribution by arranging sales to family members, friends or trusted agents who would leave control in the original owners' hands, they added.

The disputed articles require a two-thirds legislative majority--hard to attain--to set the maximum acreage that could be held by one owner, and impose a one-year delay on expropriations to give owners time to arrange a sale. Several other restrictions also undermine the reform program severely, they said.

The draft constitution was formally handed over to D'Aubuisson, the assembly president, June 20. It is to be put before the 15-month-old assembly for final approval next month, laying a legal basis for presidential elections that the United States is pushing for by the end of the year.

At the announcement Monday, however, the drafting commission said articles dealing with land reform and election schedules remained to be completed in talks among party leaders before the final assembly approval.

The land reform struggle reflects a more fundamental political split between D'Aubuisson's rightist party and the Christian Democrats, generally regarded as moderate.

Meanwhile, Washington Post correspondent Christopher Dickey reported from San Salvador that gunmen fired two bursts of machine gun fire at the U.S. Embassy Monday night and that embassy guards reportedly returned the fire. The gunmen, in two pickup trucks, also threw a bomb that exploded harmlessly in a plaza facing the embassy. The State Department in Washington said that no one was hurt and that damage was limited to two bullet holes in a corner of the building.