The nomination of Constance J. Horner to head the Office of Personnel Management should make it easier for the White House to get some of its proposed federal pay and pension "reforms" through Congress.

Horner, 43, described as a "low-key conservative" (whatever that is) is an associate director of the Office of Management and Budget. Although OPM and OMB are on the same presidential team, they have often been at odds and on very different wavelengths when it comes to proposals to cut back federal personnel costs.

OMB director David Stockman frequently complained to friends that he couldn't get some legislation through Congress because OPM director Donald J. Devine refused to make political trade-offs, or because of Devine's stormy relations with key Democrats who control the House.

Administration officials have all but given up hope of raising the federal retirement age from 55 to 65. OPM under Devine insisted that the change should be made to bring federal pension practices in line with the private sector. OMB was less interested because the first-year savings from the change would be slight, and the political battle it would have prompted would have been bloody and probably unwinnable.

But the administration is still eager to set up some kind of pay-for-performance system (as proposed by Devine) to continue health insurance cost-containment programs begun by Devine and make changes in the way federal pay is set, along lines recommended by presidents Ford, Carter and Reagan.

Horner's appointment could give the White House relatively smooth sailing in Congress, provided it doesn't ask for too much on federal employe matters.

Federal unions, which had been seeking Devine's head on a platter for the past four years, may now find that Horner is a less demanding, but perhpas even tougher opponent.