PANAMA CITY, FEB. 9 -- Showing determination to resist pressure to step down following an indictment in the United States last week, Panamanian strongman Gen. Manuel Antonio Noriega is intensifying attacks against opponents at home and abroad while apparently trying to shift the focus of the drug-trafficking charges against him.

The effort by the commander of the 15,000-member Panamanian Defense Forces has taken the form of demands by his subordinates for the ouster of U.S. military forces from Panama, the tightening of a press crackdown, legal action against some of his leading critics and veiled warnings to Panama's civilian figurehead president. Through it all, Noriega has sought to portray U.S. denunciations of him as attacks on Panama's national sovereignty.

At work against this attempt to wrap himself in the Panamanian flag and weather the storm, however, are growing popular antagonism to Noriega among this country's 2.3 million people and moves by opponents to pry open a crack in the armed forces.

An example of the anti-Noriega sentiment surfaced yesterday in a relatively minor incident that may herald something bigger in Panama's future: the emergence here of the kind of "people power" protests that led to the ouster of Philippine president Ferdinand Marcos two years ago.

When three security men in civilian clothes tried to arrest an activist of the opposition National Civic Crusade on a downtown street, he resisted and a crowd of about 200 people quickly gathered to help him. In a spontaneous demonstration, they chanted anti-Noriega slogans, jeered the security men and eventually obliged them to leave the scene without making the arrest.

The activist, Roberto Pitti, 29, was punched and beaten with rubber hoses by three men whom bystanders identified as members of Noriega's G2 military intelligence unit.

The Civic Crusade, a coalition of business, professional and trade organizations, has been at the forefront of recent efforts to mobilize opposition to Noriega and force him to step down. In a leaflet distributed last week and addressed to "military men and the Panamanian people," the group appealed to honest officers and troops of the defense forces to "rescue" their institution from Noriega and other leaders accused of drug trafficking, gunrunning and money laundering.

The charges leveled against Noriega and 15 others by a federal grand jury in Miami last week "have produced a shock in public opinion here," said Ricardo Arias Calderon, leader of the opposition Christian Democratic Party. "The country is realizing it has fallen into criminal hands."

Arias said Noriega appears to be developing a strategy to fight the drug smuggling and racketeering charges by "keeping the problem away from Panama and taking advantage of internal self-recriminations in the United States." He said the heretofore solid unity against Noriega among U.S. Democrats and Republicans now apparently risks becoming split by election-year barbs over the failure of the Reagan administration to end cooperation with Noriega sooner if it knew of his misdeeds.

Echoing the Civic Crusade's appeal, Arias said in an interview, "We are clearly hoping that there will emerge within the military a group . . . not involved in major crimes who will see the need for a change in military leadership, not only for their institution's sake, but for the country's sake."

So far, however, said Civic Crusade leader Aurelio Barria, "if there's a crack in the defense forces, it's not visible."

In a display of officer corps unity yesterday, a group of captains and majors pledged allegiance to Noriega in a televised ceremony and gave him a list of suggestions directed against domestic opponents and the United States. The officers asked President Eric Arturo Delvalle to demand the withdrawal of the U.S. military's Southern Command from Panama, charging that its presence serves to "project U.S. military power in the hemisphere and interfere in the internal affairs of friendly countries."

The 10,000-member Southern Command is charged with protecting the Panama Canal until Dec. 31, 1999, when the Panamanian military takes over responsibility for its defense in accordance with the 1977 Panama Canal Treaties. The Pentagon has made it clear it has no intention of withdrawing from Panama until then.

In a rambling speech in response to the junior officers' call, Noriega denounced the Southern Command but stopped short of demanding its expulsion, which his government clearly is not in a position to carry out.

The Southern Command "constitutes a threat to the national security," Noriega said. "For that, we reject the Southern Command as a military leadership in our territory. The Southern Command constitutes another point of aggression against . . . Panama." He added that the U.S. bases here were "an impediment to our social, economic, political and jurisdictional development."

The officers in their statement also asked Noriega to punish his predecessor as defense forces commander, retired general Ruben Dario Paredes, who has become vocal lately in demanding that Noriega step down. Paredes last week also accused Noriega of having ordered the murder of Paredes' son in an apparent drug-related killing.