President Reagan yesterday nominated Constance J. Horner, an associate director of the Office of Management and Budget, to be the next director of the Office of Personnel Management.

Horner, a low-key professional administrator, would succeed Donald J. Devine, whose directorship was marked by frequent battles with federal workers and with Congress.

The nation's personnel agency has been in turmoil since Devine was forced to withdraw his nomination for a second term and the acting director, Loretta Cornelius, began a purge of Devine's old loyalists.

Horner's selection was seen by some as the choice of White House chief of staff Donald T. Regan, who was said to prefer a pragmatic manager over an outspoken conservative such as Devine.

The choice of Horner was greeted with some surprise yesterday by federal workers' unions and on Capitol Hill. It was seen as an effort to steer a noncontroversial course, not angering the New Right conservatives who strongly backed Devine and favored Gerald P. Carmen, former head of the General Services Administration, as his replacement.

Few expected the top job to go to Cornelius, whom conservatives accused of undercutting Devine in his Senate reconfirmation hearings and who later angered some White House aides when she launched what some called her "Night of the Long Knives" against Devine's allies.

But Horner was rarely mentioned as a candidate.

"It is one of those things that just came out of the blue," said Phillip Truluck, executive vice president of the Heritage Foundation. "We had been very interested in getting Jerry Carmen in there." But Horner, he added, "certainly comes from the conservative movement and is well-known within the conservative movement."

"I don't know her. She's a neo-conservative, I gather," said Human Events editor Thomas Winter, a staunch Devine supporter. "We would have preferred Jerry Carmen."

"We hope this signals a new start for OPM away from politics and harassment," said Robert Tobias, president of the National Treasury Employees Union. "We hope she brings with her the reputation as a competent manager that she had at OMB."

As the OMB's associate director for economics and government since 1983, Horner has handled the annual budgets for the departments of Treasury, Justice, Transportation, Commerce, and Housing and Urban Development, as well as the OPM's budget.

Before joining the OMB, Horner was director of VISTA, the domestic version of the Peace Corps. Before that she was deputy assistant director for policy development in ACTION, VISTA's parent agency.

Horner, 43, has solid conservative credentials. She worked as a full-time volunteer for the 1980 Bush for President campaign, and later for the Reagan-Bush campaign.

"She is considered conservative politically, but not the zealot that Devine was," said a spokesman for the American Federation of Government Employes. "There's no swelling of opposition to her at this point."

One prominent person understood to be upset at yesterday's announcement was Sen. Ted Stevens (R-Alaska), who said he thought the White House should have consulted him. Stevens, chairman of the Senate Governmental Affairs subcommittee on civil service, had just written the White House supporting Carmen.

Stevens was an early Devine supporter, but started to waver when it was disclosed that Devine -- in the waning days of his first term as OPM director -- signed an order empowering himself to act as director while awaiting reconfirmation. That disclosure forced Devine to withdraw, citing a loss of support in the Senate.