Despite discord on the key issues of land reform and a schedule for presidential elections, the Salvadoran constitutional commission announced today it has completed work on a legal framework for new elections and democratic government in this embattled country.

The announcement, at a reception here, was designed to emphasize progress toward the goal urged on El Salvador by the Reagan administration of organizing legitimate elected institutions able to secure popular following and, it is hoped, end the three-year-old civil war.

"Thus we finish with the sacred mission that the Salvadoran people assigned to us," said Rafael Moran Castaneda, head of the 16-member commission.

But disagreement over a U.S.-backed land reform program and a presidential election schedule actually left the document incomplete in two of its nearly 150 articles, commission members said. New discussions will be held, they added, but if they fail the draft constitution will be submitted to El Salvador's 60-member constituent assembly with the disputed points to be worked out by the entire body.

The draft, scheduled for approval by the assembly next month, replaces a 20-year-old constitution that was voided by a 1979 military coup staged by reform-minded officers. It is to serve as the legal foundation for direct presidential elections that the United States is pushing for by the end of the year. Beyond that, it is intended to be the foundation of a democratic political process designed to reduce the appeal of El Salvador's leftist guerrilla movement.

Moran said the "essential modification" in the still unpublished document is its emphasis on human rights and "the human person" as the basis for Salvadoran institutions. Julio Adolfo Rey Prendes, a commission member who also is secretary general of the Christian Democratic Party, emphasized that it was drafted by elected legislators "for the first time in the history of our country," rather than being imposed by an all-powerful executive or military officers.

Ricardo Gonzalez, another commission member, said much of the new constitution was patterned after the previous document and thus, he added, "it is not a revolutionary constitution."

"You realize that everything will not be democratic and rose-colored the day after the new constitution goes into effect," he said. "But we have tried to lay the basis."

Unofficial versions published in San Salvador newspapers show 31 articles devoted to civil rights guarantees, but include provisions for their suspension in time of "invasion of the territory, rebellion, sedition, catastrophe, epidemic, or other general calamity, or serious disturbances of public order."

Under a similar provision, a state of siege has deprived El Salvador of civil rights guarantees since March 1980. Imposed by a military junta, it has been renewed monthly by the constituent assembly elected in March 1982.

Commission members nevertheless reported sharp differences over how explicitly to include land reform requirements in the new constitution and how to schedule new elections.

Rey Prendes said the Christian Democrats are pushing for detailed reform requirements within the draft constitution or a companion law agreed upon in advance. Unless the reforms are pinned down, Rey Prendes said, rightist forces could go along with the principle but dilute its application in practice later.

The debate reflects deep political differences here over the wisdom of land reform. The Christian Democrats and some military officers, backed by the U.S. government, have urged it on the country as a response to leftist challenges. But rightist landowners and politicians under the banner of former major Roberto D'Aubuisson's National Republican Alliance are seeking to slow it down or halt it altogether.

The split over an election schedule also stems from differences between the Christian Democrats and the National Republican Alliance. According to former president Napoleon Duarte, a Christian Democrat, D'Aubuisson's forces have sought to delay elections to have more time to build support while the Christian Democratic Party believes it would benefit from an early vote.