The Senate Governmental Affairs Committee will decide today whether to include an early-out in the reconciliation plan in the measure it must send the Budget Committee on Monday. Sens. William V. Roth Jr. (R-Del.) and Ted Stevens (R-Alaska) have proposed a three-month open season when employes could elect early retirement.

The early-out would be available to employes with 25 years of service regardless of age; to 50-year-olds with 20 years' service; at age 55 with 15 years' service, or for employes age 57 with at least five years of service.

Anyone within five years of being able to retire under normal regulations also could take the early-out. It would be effective 30 days after becoming law.

Pensions would be reduced 2 percent for each year the retiree was under age 55. Early retirees couldn't be replaced for three years except by presidential directive.

Although most feds like the early-out option unions have been lukewarm to it because it is linked to a hiring freeze, and because it would reduce their membership.

Roth says the early-out would cut $2.5 billion from the federal payroll and spare thousands of young workers from being laid off for economy reasons.

If the committee okays the early-out it could be included in the budget the Senate is considering for the fiscal year that begins Oct. 1. That would make an early-out possible later this year, or in early 1987.

If the early-out plan is rejected it will probably die from lack of interest.