The ruling Radical Civic Union won a convincing victory tonight according to incomplete returns from congressional elections that were widely regarded as a referendum on the first two years of President Raul Alfonsin's administration.

The government's main opposition, the Peronists, lost votes around the country after months of internal feuding and division, while small parties on the left and right made modest gains, at least in Buenos Aires.

Radical leaders interpreting returns said they picked up several additional seats in the lower house, which they already controlled and would be able to form new coalitions in several provincial legislatures that had been governed traditionally by the Peronists.

With about 70 percent of the ballots counted, the Radicals had captured 44 percent of the vote, the Peronists 25 percent and the leftist Intransigent Party 6 percent; numerous small parties split the rest.

Thousands of Radicals flooded into the streets of Buenos Aires to celebrate. The voting went peacefully but local news services reported several shootings later in clashes between Radicals and Peronists.

The vote marked the first off-year congressional election in 20 years and came nine days after imposition of a state of siege by the civilian government to combat a wave of terrorist violence.

During the campaign, the Radicals had sought to cast the election by running their candidates under blown-up images of the popular president, who still has four years left in office.

Campaign posters carried the slogan, "If Alfonsin wins, we all win," and bore circular emblems initialed with "RA" -- a play on the coincidence between the abbreviation for the Republic of Argentina and the president's initials.

Opposition parties attacked the severe anti-inflation plan introduced by Alfonsin four months ago, which effectively foreclosed economic growth, and criticized the government for not limiting payments on the $50 billion foreign debt.

At stake in the voting were half of the seats in the 254-member House of Deputies -- where the Radicals have held a one-seat overall majority -- and, indirectly, a third of the 46 seats in the Senate -- where the Peronists have held a narrow edge. Also contested were seats in provincial legislatures and municipal governments.

Congress has tended to play only a weak policy-making role, with power concentrated in the executive branch. But the vote was important for Alfonsin, who sought a solid reaffirmation of public support to strengthen his hand for expected changes in the economy and state security apparatus.

Argentina returned to democratic rule almost two years ago after seven years of military rule.

During the final weeks of the campaign, bomb explosions and phone threats against military and other targets overshadowed the debate and underscored the fragility of law and order. The government blamed the violence on right-wing extremists bent on destabilizing the country so that the military would be provoked to intervene again.

Some opposition leaders accused Alfonsin of overreacting and playing into the hands of the extremists by declaring the 60-day state of siege.

The president seemed to have stumbled into the move by first trying to invoke emergency powers in the arrest of 12 military officers and civilians said to have conspired to attack the government. Local judges then ruled that Alfonsin had to order a general state of siege to make the presidential detentions constitutional.

Although the state of siege formally suspended constitutional guarantees, the government did nothing to restrict the election campaign or other civic rights, nor has it announced any more arrests, although bomb attacks continue.

Candidates said this election fight has been one of the most cordial they can remember.

The president spent much of a 27-minute, televised address to the country last Wednesday underlining his worries about violent groups that "want to take power," although the apparent aim of the broadcast was to assure the country that he remained in control.

Alfonsin said that his first two years in office had seen a consolidation of democracy and that a period of economic growth and modernization would now begin. But he said nothing more about his economic and social agenda.

Instead he focused on the potentially disruptive problem of how to reconcile the armed forces with the rest of society after two years of military budget cuts and after the nearly finished trial of military ex-rulers.

Some Argentines worried that a lopsided Radical Party victory today could threaten the cause of democracy in Argentina.

Opposition leaders and several local editorialists have expressed alarm at suggestions during the campaign that the president and his aides are thinking of parlaying Alfonsin's popularity into a new mass movement that could dominate Argentine politics as had the Peronists in the past.

Tempting the president's advisers to think in such terms is the deep disaffection now evident in the Peronist movement.

Public support for the Peronists' Justicialist Party -- a unique alliance of trade unions, urban and rural poor and middle-class nationalists of both the left and right -- has been eroded seriously by bickering and fragmentation among its leaders.