Although government workers have shown little interest in a pension plan option that ends this month, they are lining up to take advantage of a component of the plan that allows them to cut their taxes while investing in a government-guaranteed savings plan.

Despite earlier estimates that as many as 40 percent of all eligible employes would sign up for the Federal Employees Retirement System, in fact fewer than 2 percent of the nearly 2 million eligibles have done so. On the other hand, workers are investing nearly $5 million a day in the tax-deferred savings option that started last spring. That fund is expected to pass the billion-dollar mark this month.

Only 30 days remain for those hired before 1984 to move from the old retirement program to FERS. Although a last-minute stampede is possible, it is unlikely that as many employes as predicted will make the change.

FERS covers virtually all federal workers and political appointees who have joined the government since the start of 1984.

Workers under FERS can invest up to 10 percent of their salary (or a maximum of $7,000 this year) in the savings plan. Those who put in 5 percent or more get a 5 percent tax- deferred contribution from Uncle Sam.

Employes who stay with the old retirement plan can put in 5 percent but get no matching contribution from the government unless they switch to FERS by the Dec. 31 cutoff.

The reluctance to move from a known retirement plan to one created by Congress and the White House is an indication that many people don't trust anything that politicians say is good for them. On the other hand, employes have obviously been impressed by the savings plan.

"Maybe what we need to get a big sign-up is to have the president and Congress denounce the FERS plan," a high government official suggested yesterday. "It is sad but true that the FERS, which is a very good deal for many people, is viewed with suspicion because it came into being during the Reagan administration," which many civil servants believe to be against the federal worker. Congress hasn't helped because it is still working on legislation (which may or may not be passed this year) that would make the FERS program somewhat less attractive to future federal retirees who are also looking to collect a benefit -- either as the spouse or survivor of someone entitled to Social Security.

But the same official said that the savings plan -- which is similar to but generally more generous than similar plans available to private sector workers -- "has been a winner because people can see it, figure the results and cut their tax bills while socking money away for their retirement, or for bona fide emergencies."

As of Nov. 26 the Federal Retirement Thrift Investment Board reported there were 954,973 active accounts, plus 57,000 other accounts that belong to people who have either left government but left their money in the fund, or who have stopped putting money into the thrift plan by payroll deductions.

The number of workers investing in the savings plan is greatest in agencies with big concentrations of high-paid professionals and lowest in those agencies that have large numbers of lower-paid clerical or craft employes.Events

Federal, postal and private sector unions are throwing a $1,000 per plate dinner tonight at Mel Krupin's to help in the reelection campaign of Rep. Mary Rose Oakar (D-Ohio).