Tilmon B. O'Bryant, the former high-ranking police official who retired on disability and recently took out petitions to run for D.C. City Council chairman, said yesterday that he has decided not to enter politics at this time.

O'Bryant said he had changed his mind about running because of personal reasons and a combination of factors "too complicated to explain.

"I have been in government service 31 years,," he said yesterday. "It has taken its toll on my time and energy. I'd like to have a rest first, because once I commit myself to something I'm totally committed."

At a dinner in his honor on June 9, O'Bryant had told a reporter he would asseses his chances in the political ring and then decide whether to run. If he had the organizations of front-runners Arrington Dixon (D-Ward 4) and Douglas E. Moore (D-AtLarge), O'Bryant said then, "there's no doubt I would win."

Yesterday he said that part of the reason for his decision not to run was that he realized he is "a total novice at politics.

"The only thing I have is a philosophy," he said. "You need technical ability and you need to understand the toll and time" the job would require.

O'Bryant, 58, retired as an assistant chief of police last February after 31 years service. He received a disability pension and is paid about $33,000 a year in tax-free benefits. At his retirement, his physician, Dr. Robert Dyer, said O'Bryant's high blood pressure was such that it was "absolutely essential" that he retire and avoid stress.

Yesterday O'Bryant said that he had asked Dyer last week "point black - will you advise me not to run?" it and Dyer had not objected. "He said if it's something I want to do and feel comfortable at it, to do it," O'Bryant said.

Following his retirement, O'Bryant took a job as a consultant on urban affairs to Sen. S. I. Hayakawa (R-Calif.). He resigned that position on June 9, O'Bryant said yesterday, because he wanted to devote all his energies to campaigning in the race he then expected to enter.

"I had better rest awhile; I haven't had any rest in 30 years," he said yesterday. O'Bryant said he might paint his house or take a boat trip, but that he expected to be back in public view in perhaps six months. "I won't remain mute on the affairs of the city," he said.