President Jose Napoleon Duarte plans to press his dialogue with left-wing rebels, senior government and political sources said today, and tonight he vetoed two parts of a conservative-backed electoral bill to counter recently rising pressure from the right.

The government will continue to promote efforts to "humanize" the war, a senior official said, despite what political and military sources call the resistance within the Army to the two-month-old negotiations with the left. Senior Army officers in the past week have rejected a formal cease-fire at Christmas and New Year as proposed by the insurgents, although the Army reportedly is willing to give up offensive operations during the holidays.

Duarte announced in a 10-minute television address tonight that he was using his first veto in six months as president against the conservative majority in the Legislative Assembly. He struck down clauses in the law that would have prevented his son Alejandro from seeking reelection as San Salvador's mayor, and that would have helped the nation's conservative parties to form an alliance against his own Christian Democrats.

The confrontations over the dialogue and the elections law reflected a modest resurgence by the nation's conservative forces in recent weeks in advance of nationwide elections for a new Legislative Assembly in March, political sources said. The nation's two largest conservative political parties are considering forming an alliance for the race, and they, the business community and Roman Catholic Church conservatives have stepped up criticism of the government over the talks with the left and over the nation's chronic economic difficulties.

The right appears to be reviving a bit following the twin blows this year of Duarte's election in May and his surprise opening of peace negotiations with the rebels in October. The conservative offensive is likely to limit Duarte's maneuvering room in carrying out his declared goals of reaching a negotiated settlement with the rebels and strengthening the land reform program, Christian Democratic Party sources said.

Christian Democratic leaders publicly are optimistic about their party's chances in the March elections, but one early survey showed that it is likely to gain only two seats in the assembly, party sources said. That would give it 26 seats in all and still leave it in the minority in the 60-seat chamber.

The military has indicated that it rejects removal of Army roadblocks on main roads in the countryside for a 13-day period at Christmas and New Year. The left had expected that roadblocks would be removed as part of the agreement in government-rebel talks on Nov. 30 to allow free transportation during the holidays, according to civilian leaders of the rebels.

The Army intends to maintain roadblocks, send out some patrols and carry out other routine duties during the period, according to government and military sources. "According to the constitution, we must provide security," Armed Forces chief spokesman Lt. Col. Ricardo Cienfuegos said.

Nevertheless the Army's position does not mean that serious fighting is expected over the holidays, political and military observers said. The Army appears ready to accept a de facto truce, while rejecting a formal one called unilaterally by the insurgents for two three-day periods over the holidays.

"The only thing that is accepted [by the Army] is that it is not going to carry out offensive military operations," the high-ranking government official said. He said that Duarte is willing to go ahead with the dialogue, while admitting that "it is going to be difficult."

The assembly's rightist majority sought to embarrass Duarte by passing legislation barring relatives of the president from holding certain government posts, including San Salvador's mayoralty. It forced him to choose between vetoing it and appearing to favor his son, or accepting it and sacrificing his son's career. The president himself gained popularity as the capital's mayor in the 1960s, particularly for installing the city's streetlamps.

The other section of the elections law vetoed by Duarte would have granted parties the right to place their traditional party symbols on voting ballots even if the parties are members of a formal coalition in the race. This was designed to help the largest two conservative parties -- the Nationalist Republican Alliance, or Arena, led by former major Roberto D'Aubuisson, and the once-ruling National Conciliation Party to form a coalition for the legislative elections.