BALTIMORE (AP) _ The Navy canceled tests of underwater explosives Saturday in the Chesapeake Bay after a blast killed as many as 3,000 sea trout and produced a wave of criticism from fishermen and officials.

''We were surprised we had any kill at all'' from Friday's explosion, said Diane Palermo, a Navy spokeswoman. ''We are concerned.''

The explosion came a year after the Navy promised the charges would not cause significant fish kills.

Charter boat fishermen and state officials had complained then about the planned explosions, fearing large schools of fish would be driven from the area or killed during the blasts. But the Navy decided to go ahead with the testing, saying the blasts would be monitored and would result in minimal fish kills.

Sen. Barbara A. Mikulski, D-Md., said Friday she intends to express her concern in a letter to Navy Secretary James H. Webb Jr.

''I think this is awful. Once again the Navy has underestimated the danger of what it is doing in the bay,'' Ms. Mikulski said.

A marine biologist said the number of fish killed was small compared with the total population in the bay and does not threaten to diminish the species.

A number of tests had been planned for this fall by the Naval Surface Weapons Center. Earlier in the week, another 100 fish were killed in a similar blast.

''The Navy, evidently, they do whatever they want,'' said Jack Johnson, a charter boat captain who fishes the area and has protested the Navy's presence. ''This area they are testing in is loaded with trout.''

Ms. Palermo said the Navy was considering ways of avoiding further fish kills, including moving the testing to another area and sending off small shocks that would scare fish away before the testing begins.

Three boats with fisheries biologists from the Maryland Department of Natural Resources and the University of Maryland were monitoring the Navy's work to try to minimize the fish kill.

But the acoustical equipment used to scan the underwater test area for schools of fish isn't capable of detecting fish that swim at the bottom of the bay, about 150 feet below the surface, according to Stephen Brandt, a fisheries biologist at the university's Chesapeake Biological Laboratory.

Estimates of the number of fish killed have varied from 350 to 3,500, said Brandt, whose own estimate is slightly more than 2,500.