Resistance from Panamanian soldiers and paramilitary groups was stiffer than expected, they said.
American military officials said they could provide no figures on how many Panamanian soldiers have actually been charged.
About 600 of the 4,500 Panamanian soldiers originally detained since the invasion are thought to remain in American custody.
American military officials say that about 200 Panamanian soldiers are unaccounted for and suspect that many of them may be in hiding or wounded.
In recent months, there have been confrontations between U.S. troops and Panamanian soldiers.
Panamanian soldiers detained them briefly but were talked out of taking them hostages.
Mr. Fitzwater said today that he had taken the information about the dead Panamanian soldiers from newspaper accounts.
American officials say 314 Panamanian soldiers and 202 civilians were killed in the attack last December.
General Kelly said some Panamanian soldiers had been surrendering to the United States military.
At that point, he said, the Amnericans detained 9 Panamanian soldiers and 20 civilians.