Federal prosecutors yesterday obtained a court order to seize book, movie and lecture profits from Watergate mastermind G. Gordon Liddy, who still owes the government more than $23,000 of the fine imposed after his conviction nine years ago.

Liddy, described as Watergate's tight-lipped mystery man, has written two books and launched a whirlwind career on the college lecture tour since he was released from prison in 1977, declaring himself a pauper.

The U.S. Attorney's office yesterday moved to cash in on Liddy's profits to satisfy the balance of his original $40,000 fine imposed by now senior U.S. District Judge John J. Sirica. The action came after Liddy had breached a 1980 agreement to pay off the debt in $5,000 installments every three months.

Liddy -- who once told a college audience that "I answer to my conscience; in the end, all men do" -- told government lawyers last month that he had not paid his fine because he had to pay his legal bills and his children's college education costs, sources said. He could not be reached for comment yesterday.

When he left prison, Liddy told a U.S. magistrate that he had $337,500 in debts, about $250,000 of which were in legal fees. Liddy has no bank accounts in his name, but according to tax returns, he earned more than $100,000 in 1980, sources said.

Yesterday, the federal prosecutor's office -- through the court order -- claimed first dibs on any assets of Liddy's held by the William Morris Agency, his book agent; Brian Winthrop International Ltd., the Broadway booking house that sets up Liddy's lecture dates, and St. Martin's Press, his publisher.

"We think they have some money that's due to him and we'd like it," said assistant U.S. Attorney Royce C. Lamberth, the head of the civil division in the prosecutor's office. Lamberth said yesterday that all other Watergate defendants have paid off all fines.

Lamberth said that when Liddy was released from prison, he surrendered a $3,000 life insurance policy to the government to help defray his fine. Liddy then made sporadic payments on the fine, totaling $5,000, until December 1980 when he agreed to start paying $5,000 every three months, Lamberth said.

That agreement was reached after the prosecutor's office read press accounts that described Liddy as a virtual folk hero on the college lecture circuit, recounting his personal philosophies and childhood tales of baking and eating a rat -- at a fee of $3,250 per appearance.

The first installment on Liddy's payment was due Feb. 15, 1981, Lamberth said, but went unpaid. Liddy did pay a total of $8,000 in August 1981, Lamberth said, but nothing since.

Liddy and his lawyers can go to court and challenge the government's demand for his assets, contending, for example, that other debts should be paid first. But, Lamberth said, "I think the first priority should be payment of a criminal fine that is nine years old."

As it stands now, Liddy still owes the government more than $23,000, Lamberth said, after paying off about $16,200.

At this point, Lamberth said, Liddy's options to negotiate with the government are at an end. "I will agree to payment in full. Short of that, I don't know of anything that I'll agree to," Lamberth said.

As a result of the court order issued yesterday, all three New York firms have 10 days to tally up whatever assets of Liddy's they may hold and inform the government of the amounts. If the debt is not satisfied, Lamberth said the government could move to hold Liddy in civil contempt of Sirica's 1973 order directing him to pay the $40,000 fine immediately.

"What we are frankly interested in is the money, not the contempt," Lamberth said yesterday. "If we can get the money, we'll close the books."