Office of Personnel Management Director Donald J. Devine will hold a news conference today to announce what one aide said would be a "major career change."

Aides to Devine, who is considered one of the most conservative members of the Reagan administration, declined to say what kind of an announcement the former University of Maryland professor will make. The odds-on favorite guess is that Devine will say that he will shortly leave the Civil Service hot seat job to join the president's reelection campaign or take another job in government.

Devine, who ran unsuccessfully for Maryland comptroller and who managed the Reagan-Bush campaign there in 1980, has been in hot water with federal workers and retirees since taking the top Civil Service job in March of 1981.

His proposals to revamp the federal pay structure, raise the retirement age, cut costs in the federal health program and revise promotion and layoff rules prompted several federal union leaders--and some members of Congress--to repeatedly call for his resignation. But the same proposals have drawn favorable reviews outside Washington, prompting favorable editorials in both liberal and conservative newspapers.

Devine's often abrasive style on Capitol Hill sharply contrasts with that of his Democratic predecessor, Alan (Scotty) Campbell. Campbell used charm and political persuasion--aided by Democratic majorities in both the Senate and House--to sell Congress on President Carter's controversial Civil Service reform act. Devine says the reform act mandated many of the changes he has tried to make.

Thanks to an aggressive media campaign mounted by OPM--to sell pay and pension reforms to the public--Devine has become the best-known head of the federal Civil Service since Teddy Roosevelt.

Congressional sources said yesterday that they had been expecting Devine to move on to another job in the administration. They expect the White House to court the country's nearly 5 million federal workers and retirees next year because of the election. Moving Devine, they believe, would be a first step in the healing campaign.

"He's such a perfect lightning rod, we would almost hate to see him go," a House Democratic aide said yesterday. An aide to Devine conceded that his tough policies had made him "the man you love to hate" but said it would be premature to speculate that he is moving to another job.

If Devine leaves the OPM, many moderate Republicans would like to see former Rep. Edward Derwinski (R-Ill.) fill his shoes. Derwinski lost a close race in 1980 and has been serving with the State Department. Derwinski has long been interested in federal employe matters and served as ranking minority member of the House Post Office and Civil Service Committee.

Also mentioned as a possible replacement is George Nesterczuk. He is OPM's associate director for executive personnel and management development. He has degrees in physics and astrophysics from Cornell University and Maryland, and served on the Reagan transition team at the OPM.