The Senate Governmental Affairs Committee unanimously approved legislation yesterday that would give government employes the choice of two or three retirement plans, including the chance to defer a portion of their salaries from income taxes.

The proposal, by Sens. William V. Roth (R-Del.) and Ted Stevens (R-Alaska) is expected to be cleared by the full Senate later this month and then sent to the House, which is preparing its own supplemental retirement package for the government's 2.8 million civilian employes.

Under the Roth-Stevens bill, federal workers hired before 1984 could elect to remain in the current civil service retirement program or switch into one of two options that are designed for newer federal workers, who are covered by Social Security. Here are the alternatives:

*The current civil service retirement system. It requires employes to contribute 7 percent of their salaries toward their pensions and pay the Medicare portion of Social Security. Workers may retire at age 55 with 30 years service, on benefits equal to 56 1/4 percent of their highest three-year average salary. Or they may get 80 percent of their pay after more than 41 years of service.

Pensions under this system are adjusted each year to keep pace with the rate of inflation. Employes currently covered by the system could remain under it or elect to go into one of two new options that would be offered to employes hired since the end of 1983. They are:

*Option A: Under this, workers also would pay Social Security and, if they contributed 1.3 percent of their salary to the retirement fund, could still retire at age 55 with 30 years service.

If they did not contribute to the civil service retirement fund, they would have to wait until age 62 to retire on unreduced benefits. This plan offers greater investment incentives and would allow employes to put up to 10 percent of their pay into a thrift plan, with the government contributing an additional 5 percent.

Retirees would get no cost-of-living adjustment until they reached 62; between ages 62 and 66 they would get raises that were 2 percent lower than the inflation rate, and after age 66, they would get full cost-of-living adjustments.

*Option B: Employes would pay the full Social Security tax (7.05 percent of salary) but would not make any contributions toward their civil service program. Benefits would be based on 0.9 percent of their highest five-year average salary for the first 15 years of service, and 1.1 percent for service in excess of 15 years.

Employes would have to wait until age 62 to retire on unreduced benefits, although they could retire at age 55 (with 30 years) on reduced annuities. Under the tax-deferred thrift plan, the government would match employe contributions dollar for dollar for the first 1 percent of salary, then contribute 50 cents on the dollar up to 3 percent of salary and 25 cents on the dollar up to 6 percent of salary.

Retirees would get annual adjustments 2 percent lower than the inflation rate until age 62, then full cost-of-living adjustments after that age.

Federal employes under the current civil service retirement system could stay in it or come into options A or B by the end of next year. New workers -- those hired since the end of 1983 -- would have to pick between options A and B.

House Democrats are expected to come up with their own supplemental retirement package shortly. It is expected to provide bigger civil service benefits than the options okayed by the Senate and to keep the retirement age at 55.