A U.S. district judge is expected to sign a court order today that would settle a controversial class-action lawsuit brought by inmates of Alexandria's jail to improve conditions in the 160-year-old prison.

According to an agreement set to go before Judge Albert V. Bryan Jr., the city of Alexandria, Sheriff Michael E. Norris and Virginia correctional officials have promised substantial improvements in jail conditions.

Officials also promised that plans to improve inmate health and safety programs would continue until a new $9.5 million jail opens by 1986 near the Eisenhower Metro Station close to the Capital Beltway. The tentative agreement provides that the three primary defendants pay, in equal shares, $15,000 in legal fees.

"This one is settled," said attorney Victor M. Glasberg, who represents 13 inmates in the year-old lawsuit. He said he was confident the judge would approve the agreement, which he called "an example of very responsible behavior by all the public officials involved."

"The parties have agreed to agree," Norris said of the plan, adding that he believes the city has been making all along a "good faith" effort to improve jail conditions until the new facility is built. City officials refused comment on the agreement.

If it is approved, the city would be bound to spend up to $100,000 for better fire safety in the jail located in Old Town, and greatly improve inmate medical services there. The state also would remove within 60 days 15 prisoners from the jail. The measure would relieve some of the overcrowding among the 160 or so inmates, officials said.

In a related agreement, Glasberg said the estate of Dr. Samuel M. Novak, the jail physician for more than 20 years until his death last fall, has agreed to pay the 13 inmate plaintiffs a total of $3,000 for improper treatment with the drug Thorazine for some and the denial of dental care for others.

The lawsuit, filed last summer, had sought a total of $100,000 on behalf of the plaintiffs who charged that jail conditions "constituted cruel and unusual punishment." The suit had been scheduled for trial Thursday.