Campaigning for Sunday's elections drew to a close today with members of El Salvador's crack combat battalion patrolling this uneasy capital.

As mourners heaped flowers on the tomb of the archbishop murdered two years ago today, junta President Jose Napoleon Duarte offered sharp denunciations of leftist guerrillas that seemed, once again, to rule out the possibility of a negotiated settlement to the civil war here.

When the insurgents offer to negotiate without previous conditions, as they have done on several occasions in the last year, "actually they are asking unconditional surrender," Duarte said in a press conference.

Duarte's steadfast position on talks with the left comes against a backdrop of suggestions by some of his key foreign supporters that they might not rule out such contacts after the Sunday voting. A number of initiatives also have emerged in recent days to try to rein in the violence that is overtaking Central America.

Whether Sunday's voting, by itself, holds promise of dampening the struggle within El Salvador remains an open question. The campaigning that ends at midnight tonight has been marked by vicious and bitter rhetoric, occasional gunshots and, four days before the polls open, charges of fraud and hints of revenge by leaders of the extreme right if Duarte's Christian Democrats win a majority.

In reference to pressures for negotiations from within the U.S. Congress as well as the United Nations, U.S. Ambassador Deane R. Hinton told a group of businessmen yesterday that his impression is that after the elections the new government "will have to study the options carefully. If there is a possibility to achieve peace to end the killing, if there are better opportunities to negotiate, it would be better. And we have a great interest in this because there is too much tension in Central America."

There are reports that the Reagan administration and the Sandinista government in Nicaragua may be ready to begin talks on the mounting frictions between them, many of which are directly related to the Salvadoran conflict.

At the United Nations, Nicaragua's chief of state, Daniel Ortega Saavedra, arrived in anticipation of a Security Council meeting Thursday on Nicaragua's charge of an impending U.S. invasion. Ortega said he saw "positive elements" in American peace proposals for Central America transmitted by Mexico, reported special correspondent Michael J. Berlin.

Ortega said, "Foreign Minister Jorge Castaneda communicated to us that there was such a disposition--a willingness on the part of Secretary of State Alexander Haig, and we hope this will therefore take place." The diplomatic consensus here is that the U.N. meeting was called to pressure Washington into negotiation, and no resolution will be pressed to a vote so long as the prospect of a dialogue continues. The Americans have indicated that they would prefer to wait until after the Salvadoran elections before talking with Nicaragua.

In Mexico City, the foreign minister's office quoted Castaneda as saying the United States and Nicaragua had officially asked to hold high-level bilateral talks in Managua to examine "all pending problems between them." Castaneda's office confirmed reports quoting the foreign minister as saying such talks would probably take place "very soon."

Venezuela's Christian Democratic President Luis Herrera Campins, a friend of Duarte and his strongest supporter in Latin America, said yesterday he would not close the door on support for a negotiated end to the fighting.

There are also influential figures in Duarte's own party who are discreetly sympathetic to the idea of negotiations but suggest there is no way they could make that proposal when it is thoroughly opposed by the military commanders who hold decisive power.

Duarte's words today left little apparent room for negotiations, but at the same time he never offered a flat no to such suggestions. He reiterated his longstanding position that negotiations should come in the context of elections.

"If they the guerrillas accept the rules of democracy," Duarte said, then "negotiations for peace, dialogue for peace have been always open since two years ago."

The insurgents "are blackmailing the country, blackmailing the people by saying there will not be a solution without their participation," Duarte said, adding that "they are prepared for violence, they are prepared for subversive action, they are never prepared for democratic action."

At the same time, Duarte insisted that the guerrillas do not have the strength to mount the kind of major offensive they have warned of before the elections and are playing to the collection of more than 300 journalists assembled here rather than to the Salvadoran people.

Referring to a brief firefight in a low-cost housing development near the military Ilopongo airbase this morning, Duarte told a correspondent, "They don't have the resources for anything else. A few shots and they fall back. But that's enough for the international press. They say they've taken San Salvador."

The guerrilla leadership has spoken of a major military drive that would make elections virtually impossible to carry out. The insurgents have fixed no date for the promised action, to black out the nation and bring its tranportation system to a halt, except to say that the move would come before the March 28 vote.

Because today is the anniversary of the assassination two years ago of archbishop Oscar A. Romero, a hero to the nation's leftists for denouncing military violations of human rights and a martyr to its Catholic majority, there was speculation by Duarte and others that it would be the kickoff date for the guerrilla push.

In an effort to avoid trouble, a large mass to have been said by Apostolic Administrator Arturo Rivera y Damas in the San Salvador cathedral was canceled. "Given the circumstances the country is going through, and trying to avoid massive gatherings of people, the concelebrated mass has been suspended for the sake of prudence," an archdiocese communique issued yesterday said. Smaller services were held in the cathedral and throughout the country.

Despite the shadow hanging over it, life in the city appears normal. But Salvadorans, accustomed now to extreme and haphazard violence, move through their lives with studied equanimity in the face of almost anything.

Members of the Atlacatl batallion, wearing camouflage combat fatigues and burgundy berets, fanned out through San Salvador neighborhoods this morning and U.S.-supplied helicopters with doorguns raised for action cruised just above the rooftops.

When a shot rang out somewhere near the Presidential House conference room where Duarte gave his press conference this morning, he barely flinched and seemed to take no notice.

Yesterday, a large bomb exploded a few hundred yards from the final big campaign rally for the party of right-wing retired major Roberto D'Aubuisson. The sound of the bomb rocked the national gymnasium. The crowd of 7,000 to 8,000 D'Aubuisson supporters cheered a little bit louder for their candidate.

Although D'Aubuisson's party initially appeared to be no threat to Duarte's Christian Democrats, the one-time fugitive from justice has capitalized on the difficulties of the incumbents in the midst of a civil war. His challenge is now given considerable credence and some observers have predicted that a coalition of his and other rightist groups could control the constituent assembly to be elected Sunday.