Some provisions of a Senate plan that would allow 700,000 federal employes to retire this year were endorsed yesterday by the director of the Office of Personnel Management. But she cautioned that the plan must contain safeguards to protect key government operations from being gutted by a mass exodus from government agencies.

The legislation, sponsored by Sens. William V. Roth Jr. (R-Del.) and Ted Stevens (R-Alaska), would lower federal age and service requirements between July 1 and Dec. 31 and triple the number of employes who could retire. During those six months, one-fourth of the government's work force would be eligible to retire.

OPM Director Constance Horner told the Senate Governmental Affairs Committee that the bill proposes a humanitarian and cost-efficient way of cutting the federal payroll in an era of belt-tightening.

But she said the administration needs flexibility to deny early retirement to groups of workers or agencies where massive retirements would be disruptive. She also asked that the president have authority to fill some vacancies that would be created.

Professional groups and unions representing employes also asked for provisions to prevent agency programs from being crippled -- but for different reasons: They said they didn't want mass retirements used as an excuse for handing over work to private contractors.

Committee Chairman Roth said his bill is a first draft and subject to revision.

Normal civil service rules allow retirement at age 55 after 30 years of service, at age 60 after 20 years' service or at age 62 after five years of service. Benefits are based on salary and length of service. The Roth-Stevens plan would let employes retire between July and Dec. 31 at any age after 25 years' service, at age 50 after 20 years' service, at 55 after 15 years and at age 57 with five years' service. Pensions would be reduced 2 percent for each year the retiree was under age 55.

Rosslyn S. Kleeman of the General Accounting Office said early retirements "could minimize or substitute" for layoffs and save employes with less seniority -- many of them women or minority group men -- from being fired. But she said exits through the retirement window could cost the government many of its key employes. Replacing them would be time-consuming and costly, she added.

She said that although few of the Postal Service's 650,000 jobs are in danger, upwards of 100,000 of its employes could retire if the Roth-Stevens bill became law. A senior postal official testified that a mass exodus could force the service to resort to costly overtime to move the mail.

Jerry Shaw of the Senior Executives Association said many of the government's top-paid career employes could be expected to take the early out if offered, and that their departure could "shake the foundations of many agencies and seriously jeopardize" their missions.

Kenneth T. Blaylock, president of the American Federation of Government Employees, said he welcomed efforts to eliminate the need for layoffs. But he said a proposed limitation on hiring over the next five years must be modified.

"If the premise is that the government can reduce personnel by 10 to 15 percent without reducing the role of government commensurately, the bill is greatly flawed," he said.

The bill is expected to be revised before the committee approves it. The House has not yet begun to consider an early retirement plan.