The wife of Federal Bureau of Investigation Director William S. Sessions accompanied her husband on 17 official trips aboard government aircraft but paid for only one flight, the General Accounting Office said yesterday.

Alice Sessions accompanied her husband on business trips from Washington to destinations including Key West, Fla.; Williamsburg, Va.; San Francisco, and New Orleans from Aug. 11, 1988 through July 31, 1989, according to the GAO report.

While it did not question propriety of the trips, the report criticized the Justice Department for failing to study the cost of using aircraft seized from convicted criminals to transport Sessions and Attorney General Dick Thornburgh.

The GAO said it believed the department could save money by leasing planes.

FBI spokesman Robert Davenport said Mrs. Sessions did not reimburse the agency for the trips because she was accompanying her husband on official business.

Davenport said Mrs. Sessions did pay the FBI $280 to cover one leg of a trip that included a stopover in San Antonio for personal business.

Sessions made 36 trips, generally to visit FBI field offices and to make speeches to judicial and police groups. Thornburgh made 39 trips during the period aboard the government-owned aircraft, mainly to give speeches and attend meetings.

Five months after the GAO began its study, Thornburgh reimbursed the Justice Department $2,128 for eight trips his wife took on the government planes, the report said.

The payment included $1,371 for six trips that Mrs. Thornburgh took during the 12-month period reviewed by GAO, the report said. Thornburgh also repaid the government $1,032 in 1989 for personal trips he and his family members took aboard the aircraft.

Justice Department policy does not require Mrs. Thornburgh to pay for trips on official flights "if there is an empty seat and the government would incur no extra cost," department spokesman Dan Eramian said.

The GAO study said the Justice Department failed to follow government guidelines when comparing cost of using government aircraft seized from convicted criminals with cost of using leased planes to transport Thornburgh and Sessions.

The Justice Department's analysis, conducted after the GA0 began its study, showed that the government was saving $500,000 a year to use the seized aircraft instead of leasing planes.

"If we had leased an aircraft and spent an extra half million a year, we would have received a larger dose of criticism," Eramian said yesterday.