Fairfax City Manager George E. Hubler Jr. resigned recently under pressure after an investigation by the Fairfax prosecutor found that Hubler had bought himself a private health club membership with city funds.

Robert F. Horan Jr., Fairfax commonwealth's attorney, and the Fairfax City Council -- which conducted a separate probe -- determined that Hubler acted improperly last January when he issued a voucher for $550 in city funds for a membership to The Sporting Club in McLean.

"I did it," Hubler said yesterday. "I didn't have the explicit authority from the council. I guess in retrospect I should have checked with them. I didn't, so I have to suffer the consequences."

The 45-year-old Hubler said he spent about $250 of his own money in addition to the $550 in city funds in order to test the weightlifting equipment two or three times during January.

Hubler said he joined the club to evaluate its Nautilus exercise equipment, which is similar to equipment the city was considering buying as part of a council-approved $7,000 fitness program for firemen and policemen.

"I'm a detail man," Hubler explained. "I didn't want to rely on salesmen or anything. I wanted to check this equipment out myself."

In a statement released yesterday, the Fairfax City Council said, "From its investigation, the council unanimously concluded that the manager had overstepped his authority in securing membership without express council approval."

The investigations of Hubler began last March, after Fairfax City Council member Mary Roper asked Horan to clear up some questions she had about a copy of a city check made out to the health club. She said she found the check while routinely examining city budget records.

"I really did not think there was anything illegal about it when I first received it," said Roper. "I know the city was planning to buy weightlifting equipment for the police and fire departments as part of a fitness program, but then I called the health club and it didn't add up. I called the commonwealth's attorney office and asked them to investigate."

After learning of the investigations, Hubler reimbursed the city for the $550. On Sept. 15, Horan told council members in an executive session that "it was a close case" and that prosecution of Hubler would be hard because the city's charter may have given Hubler the right to spend the money. Horan said he would not prosecute Hubler if he resigned.

The council unanimously concluded that Hubler had not tried to defraud the city, but that his action warranted his resignation. Hubler resigned soon after the council meeting. Yesterday's council statement said the incident was not made public because it may have hurt Hubler's ability to find another job.

Hubler was assistant city manager and budget director in Alexandria for four years before taking the Fairfax City job in 1974. Yesterday, he described the county investigation and his forced resignation as "a little heavy."