PANAMA CITY, MARCH 2 -- Scattered street protests and several bomb threats at the Panama Canal today raised the intensity of a confrontation between Panama's military-backed government and opposition groups as a general strike spread into its third day.

The actions came as the United States sought to exert economic pressure on the regime of military strongman Gen. Manuel Antonio Noriega by helping prevent his representatives from withdrawing Panamanian government funds held in U.S. banks.

Noriega last night called the U.S. action "another sign of North American aggression" against "a friendly country such as Panama," Reuter reported. Manuel Solis Palma, installed as acting president Friday at the instigation of Noriega, said he found the move incomprehensible.

In another development, government officials and military officers denied an opposition legislator's statement that a purge was under way in the top ranks of the Panama Defense Forces to remove officers suspected of insufficient loyalty to Noriega.

Diplomatic and independent Panamanian sources also said there was no evidence of a purge. But they confirmed that at least one major, who is related to a retired general opposing Noriega, was forced to resign within the last several days.

The strike, called by the opposition National Civic Crusade to protest Noriega's rule, appeared to solidify as most shops, businesses and financial institutions in the capital remained shut for a third day. Doctors reportedly joined the strike, accepting only emergency patients.

In a downtown neighborhood -- where residents yesterday protested a raid by government agents on an opposition radio station -- Noriega's opponents burned a government truck and set up street barricades of burning trash. In other areas, protesters set fire to tires in the streets, and riot police known as "the Dobermans" were called out.

About 50 Civic Crusade members marched through city streets chanting anti-Noriega slogans in an effort to galvanize the largely passive resistance to what the opposition calls the "narco-military dictatorship." Marchers said they hoped to encourage the Civic Crusade, which has been reluctant to confront the security forces, to take their protests to the streets.

Civic Crusade leaders said tonight that the strike would continue Thursday, although some food stores and banks would reopen.

At the Panama Canal, anonymous callers phoned in at least three bomb threats during the day, forcing the evacuation of the administration building, the Miraflores Lock visitors' center and the personnel office, officials at the canal said. Nevertheless, they said, the canal operated normally again, without unusual absenteeism.

Canal workers reported, however, that some slowing of the waterway's operations and increased absenteeism did occur as a result of sympathy for the general strike among the 7,400 employees. One workers' representative said the highest absenteeism occurred in the canal's dredging operations and at the Miraflores Lock.

The U.S.-run Panama Canal Commission, determined to stay out of the country's political turmoil, has warned workers that any strike activity will be dealt with severely. Since the canal employees, including 6,141 Panamanians, are U.S. federal workers, any strike by them would violate U.S. law and make them subject to dismissal, officials said.

Yesterday, an anonymous bomb threat forced the evacuation of 400 employees from the Panama Canal headquarters for about two hours. A separate bomb threat called in to the Midland Bank here yesterday forced the evacuation of the U.S. Information Service offices located in the same building, an embassy spokesman said.

At a news conference, Solis Palma defended the ouster of President Eric Arturo Delvalle for trying to replace Noriega as commander of the Defense Forces. Solis Palma called an appeal by Delvalle to the public not to pay their debts to the government "a seditious act."

Delvalle, who is still recognized as president by the U.S. government, remained in hiding to avoid arrest and deportation by the military.

Solis Palma, Government and Justice Minister Rodolfo Chiari and Police Chief Col. Leonides Macias denied reports of a military purge. "These are inventions to confuse the people," Macias said.

However, reliable diplomatic and Panamanian sources said Maj. Moises del Rio, a cousin of retired general Ruben Dario Paredes, was forced to resign Saturday after returning from an assignment as military attache in Peru. Paredes, Noriega's predecessor as commander of the 15,000-member Defense Forces, has called for Noriega to step down.