Government troops Monday surrounded bases and buildings seized before dawn by mutinous soldiers in an uprising two days before President Bush was scheduled to visit.

President Carlos Menem declared a state of siege, suspending constitutional guarantees and giving his government sweeping powers to ensure public order. His government demanded that the rebels surrender unconditionally.Bush, in Brazil, indicated he had no plans to cancel his visit to Argentina, and the military said the situation was being brought under control. The rebels said they were not trying to overthrow the government but were trying to force changes in the way the military was run.

The uprising, the fourth military revolt in Argentina in four years, began when insurgent soldiers seized part of the downtown army headquarters, several coast guard buildings nearby, a tank factory 16 miles to the northwest and infantry base five miles to the north. Loyal troops tried to retake the installations, but by afternoon the rebels were still holed up in the buildings they seized. The army said at least three loyal soldiers were killed and 14 wounded in the fighting.

Police sealed off major roads in Buenos Aires, a city of 10 million people. Federal police banned public gatherings, and the Economy Ministry declared a bank holiday.

The army said a total of 200 rebel soldiers were involved, but rebels claimed to have 700 followers at several bases, including a tank battalion in Entre Rios Province, north of Buenos Aires Province.

The private news agency Noticias Argentinas said government troops were mining the exits from the tank factory to prevent the rebels from driving tanks out.

It also said the government troops had dynamited a bridge and blocked a tunnel that cross the Parana River north of the capital to prevent a column of rebel tanks and armored vehicles from leaving Entre Rios Province.

The army chief of staff, Gen. Martin Bonnet, said in a communique that the army is "under the orders of their commanders, except for small groups that are being put under control."

In the capital, rebels fired at and hit a helicopter carrying Vice President Eduardo Duhalde as it landed on the roof of Government House, two blocks from the downtown army headquarters. Duhalde was unhurt.

Gunfire was heard in the port zone two blocks to the other side of Government House, where Menem and Duhalde have their offices.

Bush, who arrived in Brazil Monday, said his visit was still on. "I have no thoughts of changing my plans. I have great confidence in the security there," he told reporters in Brazil.

The insurrection was the first in Argentina since Menem took office in July 1989. He is the country's second civilian president since the military ceded power in 1983.

All of the previous insurrections have been by officers who declare themselves nationalists and demand pay increases, pardons for rights abuses during the 1976-83 military regime, and changes in the military high command.