ANCHORAGE, SEPT. 22 -- Federal prosecutors assert that Exxon Corp. knew for years about allegations that fired Exxon Valdez skipper Joseph Hazelwood regularly hosted drinking parties and tossed his empty whiskey bottles overboard.

According to the government, Exxon Corp. knew since 1985 that Hazelwood was diagnosed with two medical problems -- episodic alcohol abuse and a type of mood disturbance called dysthymia.

The government also accused Exxon of failing to monitor Hazelwood after he was treated for alcohol abuse in 1985. Monitoring would have revealed that he continued to drink while on duty up to the night the tanker struck Bligh Reef, spilling nearly 11 million gallons of crude oil into Alaska's Prince William Sound, the prosecutors said.

"The Exxon medical department had a duty to ensure that Hazelwood was fit to command oil tankers," prosecutors said. They called his alcohol abuse and dysthymia problems "serious" and "known to impair judgment."

These allegations and others about Hazelwood's alleged on-board drinking were contained in the government's response last week to Exxon's request that all criminal counts against it be dropped.

Exxon was indicted in February on five counts related to the March 1989 spill. If convicted, the company could be fined more than $600 million.

Justice Department lawyers said Exxon Shipping's president only reluctantly agreed to give Hazelwood back his job as tanker master after treatment for alcohol abuse.

Prosecutors said had Exxon monitored Hazelwood, it would have learned he lost his driver's license months before the tanker disaster on a drunken-driving conviction.

In March, Hazelwood was acquitted of being drunk and reckless and was convicted by an Alaska jury of one misdemeanor charge of negligent discharge of oil. The conviction is under appeal, along with his sentence of $50,000 in restitution and 1,000 hours cleaning beaches at Prince William Sound.

The Coast Guard dismissed its case against Hazelwood in August.