SEATTLE, OCT. 19 -- Government officials have quietly ordered the killing of hundreds of birds, some seals and perhaps other mammals for studies that could strengthen their court case against Exxon for the 1989 oil-tanker spill in Prince William Sound.

"Pretty incredible, isn't it?" said Steve Goldstein, a spokesman for Interior Secretary Manuel Lujan Jr. "The secretary did not know of this in advance and would not have approved it if he did."

Federal officials in Alaska confirmed that they authorized the killing of birds for at least eight studies to determine how many animals were killed by the oil spill. The bird carcasses, some of them oiled to simulate the spill, were then tossed into Prince William Sound and tracked.

In one study this year, 250 or more birds were shot. In the others, federal officials indicated the numbers were somewhat lower -- a few dozen for each study. By tracking the movement of the bodies through the water, the studies sought to devise a formula for determining how many birds may have succumbed to the effects of oil.

Alaska officials confirmed that they too "collected some animals" in preparation for a damage suit against Exxon. But a state official said lawyers in the case ordered that no specifics be released until the legal implications are studied. All that is known is a previously disclosed kill of 10 harbor seals, including three pups, in Prince William Sound in 1989.

In addition to seals, federal authorities said that the state of Alaska may have killed river otters, deer and other mammals as well as an unknown number of sea ducks as it builds a scientific foundation for its litigation.

Meanwhile, in Anchorage, a federal judge denied a dozen motions made by Exxon Corp. and Exxon Shipping Co. to dismiss criminal charges stemming from the Exxon Valdez spill.

Trial has been set for April 10, more than two years after the tanker left the port of Valdez and ran aground on a marked reef in Prince William Sound, spewing more than 10 million gallons of oil and fouling fishing grounds and wildlife habitats.