Tilmon B. O'Bryant, a former high ranking city police official who is receiving $33,000 a year in a tax-free disability pension because of high blood pressure, has been working on Capitol Hill for one month and yesterday took out petitions to run for City Council chairman.

O'Bryant, 58, was an assistant chief of police when he abruptly applied for disability retirement three months ago. At O'Bryant's retirement hearing his physician testified that he suffered from hypertension, and said that, because of the stress of O'Bryant's job, he would be subject to a stroke if he continued working.

O'Bryant could not be reached for comment last night. His physician, Dr. Robert F. Dyer, said he knew nothing about the situation and could not comment.

Retirement board members interviewed yesterday expressed surprise and dismay. "He told us he was not going to do anything, that he had to take it easy and avoid pressure," said one board member. "This is pressure, pressure, pressure. I can't believe it."

O'Bryant was hired one month ago as a part-time urban affairs consultan to Sen. S. I. Hayakawa (R-Calif.). Hayakawa said yesterday that he has known O'Bryant for at least 12 years and that he saw nothing wrong with O'Bryant seeking public office in spite of his disability claim.

"If he thinks he can take a different kind of pressure that's fine with me," the freshman senator said. "I changed from one type pressure to another myself."

O'Bryant appeared at the city's Board of Elections office shortly after 8 a.m. yesterday to sign up for the council chairman's race and take out petition forms.He will need 1,826 signatures to qualify as a candidate, and can file no earlier than June 10 or later than July 5.

City Councilmen Arrington Dixon (D-4) and Douglas E. Moore (D-At Large), and a citizen, John R. Martin, already have taken out petitions for the $38,444 a-year position.

Hayakawas said yesterday he met O'Bryant in 1966 when he was then an English professor in San Francisco and came to Washington for a seminar on civil disorders. The two kept in touch since then, Hayakawa said.

"Whenever I came to Washington I would drop in and see him and he would drive me around town and show me the burned out areas and show me what the problems were," Hayakawa said. "He was very experimental-minded. He will bring (to the Hill) a kind of intense knowledge of urban affairs, a knowledge of black communities."

A spokesman for the senator said O'Bryant would concentrate on the high unemployment rate among minority youths, nationally and particularly in California, and in that regard has made one trip to Los Angeles.

The spokesman, Janice Barbieri, said O'Bryant could set his own hours and had read O'Bryant could set his own hours and had been in the office two or three times a week.

"This is not a pressure type job, she said in response to a reporter's question. "He certainly won't have the pressure here he had day-in and day-out" in the police department.

Asked whether O'Bryant's retirement was consistent with his move toward public office, Hayakawa said he had read O'Bryant's letter to the editor, published March 4 in The Washington Post, "and I thought that was a very dignified and full explanation of why he is retiring on disability and thought there was nothing wrong with that."

In that letter O'Bryant cited his service to the community in his 31 years with the police department, and said that media attention on his disability was motivated by racism.

O'Bryant's disability retirement was the subject of considerable publicity in part because it came at a time when the disability retirement system was under intense scrutiny by the press and Congress.

Eighty-two percent of the retired policemen in the District of Columbia have gone out on disability, which entitled them to a tax-free lifetime pension. This percentage is far greater than in other major cities, the result of a system that Sen. Thomas F. Eagleton (D-Mo.) has said is the "premier ripoff" in the country.

Legislation pending in Congress would make it more difficult to retire on full disability.

O'Bryant's disability retirement came at about the same time as that of police chief Maurice J. cullinane (knee) and fire chief Burton Johnson (back). O'Bryant's retirement with full disability drew special criticism from the police union because O'Bryant had routinely turned down sick leave requests from the rank and file, and was a well-known jogger who had been seen running a few weeks befor his retirement announcement.

In mid-February he put in for retirement. He cited in his letter to the editor what he said was a recent deterioration in his physical condition and he quoted Dr. Dyer as saying, "Chief, for several years I have told you that your blood pressure is a dangerous thing to be toying around with and you should not be working . . . It was at that point that I decided to follow the advice my clinic physician had given for years, and retire as soon as possible."

Percy Battle, the chairman of the Police and Firemen's Retirement and Relief Board, said yesterday that because O'Bryant is over 50 years old, he could take any job he wished, at any salary, as he is no longer subject to any restrictions by the board.