A Prince George's County Council member expressed alarm yesterday that County Police Chief John W. Rhoads is seeking to retire with extra disability pay because of a back injury.

"This disturbs me," said council member Sue V. Mills at yesterday's weekly council meeting. "I thought the justification for the new retirement plan and the disability plan was because police work is . . . hazardous . . . John Rhoads doesn't have a hazardous job."

Rhoads is seeking a disability pension that would pay him 70 percent of his salary-about $29,000 a year.

"This violates the intent of the contract," declared Mills. "The man's 43. So am I. He has no more hazardous job than I have."

In formally announcing his retirement yesterday, Rhoads said he hopes to return to police work some day.

Saying he is taking pills to combat his pain, Rhoads told reporters that "time or an operation may heal this injury to the extent that I can take a job with a smaller agency where the demands are less, both physically and mentally."

If Rhoads did another job after retiring on disability, he would face a reexamination to determine whether he would lose his 70 percent pension and receive only the standard 50 percent retirement pay.

Rhoads initially injured his back in 1971 during a high-speed chase. He injured it again when he slipped on a patch of ice in 1973, and most recently when he slipped after addressing his men at their union headquarters last month.

Rhoads has been chief for four years, presiding over the force during a tumultuous period marked by progress in polic-community relations and controversy over race relations between the force - 93 percent white - and the county's growing black population.

Speculation on a successor to Rhoads has centered on former FBI agent Jack McHale, who is currently an aide to County Executive Lawrence J. Hogan.

Asked yesterday if McHale would be considered, Hogan replied, "The man has 30 years's experience with the FBI. You certainly can't discount him."

Rhoads said he would not play any role in choosing his successor, but hoped he would come from inside the department. Although Hogan said that the department's three lieutenant colonels-Vincent duCellier, John Magruder and Joseph D. Vasco - would be considered, police insiders said that, for various reasons, none of the three is thought likely to be named chief.

Besides making it clear that McHale was a candidate, Hogan would say only that former Montgomery County chief Robert J. diGrazia would not be considered for the position.

Rhoads' decision to retire on disability came after Montgomery County Executive Charles W. Gilchrist chose the D.C. Assistant Chief Bernard D. Crooke after firing diGrazia.

Privately, Rhoads told friends that he would have liked the Montgomery job.

It was only a week after Crooke was named Montgomery police chief that Rhoads reinjured bis back, sealing his decision to retire on disability. A county medical review board will meet tomorrow to consider his disability claim.