Exxon Is Asked to Pay More for Valdez Study : Environment: State and federal officials say another $20.4 million is needed for the oil damage assessment.

Officials of the federal government and the state of Alaska asked Exxon Wednesday to put up another $20.4 million to continue the damage assessment of last year’s oil spill in Prince William Sound by the supertanker Exxon Valdez.

Under an agreement signed a month after the March 24, 1989, accident, the company provided $15 million to begin the detailed study of spill-related damage to the pristine natural resources of the area. But officials of the Department of the Interior said Wednesday that more money was required because of the scope of the disaster.

Long-term studies are expected to continue for years, but sources said the analysis of the immediate impact of the spill must be pushed aggressively because a delay in final damage assessment would pose problems if the government decides to take Exxon to court.

The damage assessment is being carried out by a panel of trustees consisting of Interior Secretary Manuel Lujan Jr., Agriculture Secretary Clayton K. Yeutter, National Oceanic and Atmospheric Administration chief John A. Knauss, and Alaska’s commissioner of fish and game, Don W. Collingsworth.

Although the government agencies are still in the first phase of their damage assessment, Exxon already has spent some $2 billion cleaning up the oil that drifted ashore, fouling beaches and killing large numbers of mammals and water birds.

The captain of the Exxon Valdez, Joseph Hazelwood, is awaiting trial on felony charges of criminal mischief and misdemeanor charges of reckless endangerment, operating a vessel while intoxicated and negligent discharge of oil.

Hazelwood is no longer employed by Exxon.

In its letter advising Exxon that it wants the additional $20.4 million, the commission said it expects to have spent $35.4 million by March 1 trying to determine the impact of the disaster.

Under the oversight of the federal-state council, Interior Department experts are evaluating the damage to public lands and wildlife. NOAA is studying the effects on marine species, and the Agriculture Department is evaluating the impact on forests. The Alaska Fish and Game Commission is leading the state’s assessment of economic damage.

Lujan commended the oil company for “promptly and positively” responding to the commission’s first request for payment last April, and he said he was “hopeful the company will follow through now as we near completion of this initial step in the assessment process.”

Exxon officials later issued a statement in Houston saying the company had not had time to study the request but suggesting that the damage assessment has not been properly conducted.

“The unanimous opinion of these studies, based on public comment, is that they are poorly designed and fail to address restoration of the environment as they should,” the company said.

So far, Exxon added, it has received no government accounting for the use of the first $15 million.

The council issued a draft damage assessment plan last summer, and public comments on it are now under review.

Under the law, state and federal officials have the authority to assess the damage to natural resources by the spill of oil or toxic substances. Responsible parties are liable for payment for the assessment as well as damages and restoration.

Interior Department sources said Exxon can be expected to return to the cleanup job in Prince William Sound not only next spring but for some years to come.

More than 11,000 workers were involved in the cleanup at its peak last summer.