The typical retired civil servant would lose $1 a day in future pension income under the Carter administration's plan to limit them to a single cost-of-living (COL) adjustment each year, instead of inflation adjustments every six months.

Senate hearings begin this morning on the controversial proposal already cleared by the budget committees of the Senate and House. The plan would give federal-military retirees one COL adjustment each year. They now get two raises a year to help keep pace with inflation.

Metro Washington has already nearly 100,000 retirees, and their annuities are a big chunk of the local economy.

Carter aides today will endorse the concept of a single COL adjustment each March. They will argue that it would be more equitable, and would save the federal retirement system around $640 million each year.

Moving to a single COL raise yearly would cut compounding costs, and make retirees wait twice as long for an inflation increase. Based on an annual inflation rate of 15 percent (and that is a conservative figure these days) it would cut spendable, in-pocket income from raises for the typical $800-a-month civilian annuitant more than $360 a year. The loss would be greater if inflation increases.

Retirees now get COL adjustments -- as measured by the Consumer Price Index -- every six months, in March and September. In September 1979 retirees got a before-taxes raise of 6.9 percent.This month retirees got a 6 percent increase based on the March 1980 adjustment. That worked out to about $48 a month per retiree before taxes.

Under the administration proposal, government retirees would get a COL raise every March, payable in April. Social Security benefits already are adjusted annually, each July.

The COL cutback is of major concern to federal and postal unions, retirees and people who eventually will retire from government. Groups representing active and retired workers have raised more than $3 million to fight various congressional "assaults" on the federal retirement program, including the COL cutback and proposals to force federal and postal workers to go under social security. Although President Carter has not taken a stand on the civil service-social security linkup, officials today will endorse and argue in favor of the single annual COL raise for all retirees.

Hearings begn at 9:30 a.m. before the Civil Service Subcommittee on the Senate Governmental Affairs Committee.