PANAMA CITY, OCT. 18 -- Panama's U.S.-backed government said today that it had uncovered an apparent plot to topple President Guillermo Endara that was to start with a takeover by rebel police units of the northwestern province of Chiriqui.

The president's office issued a statement quoting a senior police official arrested in connection with the plot as saying that it was led by a former national police chief, Eduardo Herrera, a colonel who was retired last August. Herrera's whereabouts were not immediately known.

"The goal was to take over the province . . . as part of a nationwide plan," Capt. Carlos Ivan Moreno, Chiriqui's deputy chief of police, said, according to the presidential statement. It said the plot, originally planned to take effect Tuesday, had been "frustrated" by loyalist police officers.

There were conflicting accounts over the seriousness of the attempt to oust Endara. Earlier, Vice President Ricardo Arias Calderon, who is also justice minister and responsible for the country's public security force, denied that there had been a coup attempt. A spokeswoman for the attorney general refused to describe the aborted plot as a coup attempt, calling it instead a plan to "destabilize" the government.