Fairfax County is considering taking steps to tighten procedures for verifying the credentials of prospective employes, County Executive J. Hamilton Lambert said yesterday.

The policy review comes on the heels of the forced resignation two weeks ago of R. Barry Thompson as director of design review after county officials were unable to verify his educational record as he had stated it on his resume.

Thompson was told to resign or be fired from his position as the third-ranking official in the county's Department of Environmental Management after county officials discovered he had neither the bachelor's degree in engineering nor the master's in business from the University of Maryland that he had listed on his resume. He resigned from the $54,000-a-year job.

Lambert said he has asked Fairfax personnel director Cornelius J. O'Kane to review current procedures and recommend new steps for checking future employes' resumes.

He stressed, however, that any new measures would be limited and would apply to prospective rather than current employes. He said an indiscriminate check of current workers would be prohibitively expensive and unlikely to uncover many instances of falsified credentials.

"I just do not believe it is a widespread problem," Lambert said. "The probability of someone falsifying their credentials would be extremely low."

Lambert said he does not favor checking the resumes of current employes or of applicants for most unskilled and blue-collar jobs.

If the county were to implement a new policy of checking credentials of job applicants, Lambert said, it would apply to managers, technicians and skilled positions.

Fairfax County has about 9,000 workers, not counting its school employes. Currently, the most thorough background checks are done for police, fire and other protective employes.

O'Kane said "a great deal of checking" should be done for custodial and caretaking positions, such as those in the mental health field.

O'Kane said any new procedures probably would not include a review of credentials for internal promotions, and therefore would be unlikely to prevent a case like Thompson's. Thompson had been hired by the county in 1981. Before that, he worked for the county water authority, an independent agency, for four years.

Fairfax officials say they cannot remember any similar cases among county employes.

With the publicity that has surrounded the issue recently, Lambert added, applicants for county positions "are probably double-checking their birthdays."

"Of course," he added, "you don't have to worry about my education . . . because I don't have any." Lambert graduated from Loudoun County High School in 1959. He did not attend college.