Senate hearings begin next Thursday on a bill that would allow government workers to take advantage of an early retirement option between July 1 and Dec. 31.

At the same time, the Roth-Stevens bill would impose a virtual hiring freeze on the government over the next five years.

The proposal, by Governmental Affairs Committee Chairman William V. Roth Jr. (R-Del.) and Sen. Ted Stevens (R-Alaska), would temporarily suspend government age and service requirements for retirement.

In most cases, the earliest a federal employe currently can retire is at age 55 after 30 years' service. About 200,000 workers could retire now, if they wanted.

For six months, that number would double under the Roth-Stevens bill, which could permit retirement in an employe's early forties.

Roth and Stevens say the purpose of their bill is to encourage older workers to retire, which would minimize the need for massive layoffs because of budget cuts required by Gramm-Rudman-Hollings formulas.

They said their legislation would spare the jobs of thousands of younger workers who might otherwise be fired beginning in October, when agencies are required to make trims.

It would allow employes to retire at any age after 25 years of service, at age 50 after 20 years' service, at age 55 after 15 years' service or at age 57 after five years of service. Annuities would be based on the employes' salaries and time in government, and would be subject to a 2 percent reduction for each year the retirees were under age 55.

The lead witness at the hearings on the bill will be Office of Personnel Management Director Constance Horner.

Horner has recommended that the White House support the Roth-Stevens bill, but with major modifications.

She called for shortening the period to three months and limiting early retirement to employes who have 25 years' service, or those age 50 with at least 20 years' service.

The OPM director also suggested that government agencies be allowed flexibility to fill some of the key vacancies caused by the early retirement.

Although most federal employes welcome the retirement option, union leaders have expressed reservations about it. Several of them have charged that this is just another ploy to cut federal employment. They also have been asked to testify at the hearings.

The House Democratic leaders, who are often sympathetic to federal and postal union leaders, are waiting to see what kind of bill the Senate comes up with before taking a stand.

Senate sources have said that if the bill isn't approved by Congress and the White House by July 1 -- and it probably will not be -- they would anticipate that the period called for in the legislation will be changed. Retiree Raise

The House compensation and employee benefits Subcommittee is expected to clear a bill today that would guarantee federal retirees a cost-of-living adjustment next January. Federal and military retirees were due a 3.1 percent COLA this year, but lost it because of the Gramm-Rudman-Hollings act.

Rep. Mary Rose Oakar (D-Ohio), who heads the subcommittee, already has more than 250 cosponsors for the proposal, more than enough to guarantee House passage.