Only 1.5 percent of federal workers have chosen to join the Federal Employees Retirement System, one of the most generous pension plans ever offered by a major employer in America, the Office of Personnel Management said yesterday.

The failure of the new retirement system to attract members astounds pension experts, who estimated last year that 40 percent of federal workers would be better off joining the new system than remaining in the Civil Service Retirement System.

"It is a sad commentary on the government work force," said pension consultant Jamie Cowan of Government Retirement & Benefits Inc. "It is a tragedy for many individuals who will lose a lot."

The low response to a $3 million barrage of information about the new system is blamed on distrust, complexity and inertia.

Employes see it differently. "Why change a good thing when you have it?" said Trudy Beckwith, a personnel assistant with the General Services Administration. "A lot of people think the devil you know is better than the devil you don't know, and for me I saw no economic advantage in making the change," said Robert V. Hoobing, a media relations specialist for the Postal Service.

Although the one-time open season for transfers ends Thursday, Congress is likely to be asked to give employes a second chance to switch. Rep. William D. Ford (D-Mich.) told postal workers recently that he wouldn't close the door to another open season on transfers, but interest so far has been slight.

Virtually all federal and postal workers hired since Jan. 1, 1984, are automatically members of the new Federal Employees Retirement System (FERS), which has three parts: Social Security, a small pension and a tax-deferred savings plan under which the government will match, roughly, the first 5 percent of an employe's salary. The prior system has no thrift plan or Social Security retirement, but larger pensions.

The thrift plan is more generous than 97 percent of such plans across the country. Most employers contribute only 50 cents to their employe thrift plan for each $1 saved by the employe up to about 6 percent of a worker's salary.

Under the new federal plan, the government automatically contributes an amount equal to one percent of an employe's salary, matches dollar for dollar the employe's contribution for the first 3 percent, and contributes 50 cents on the dollar for the next 2 percent. Employes can save up to 10 percent of their income and shelter it from taxes until retirement.

But when the FERS doors were thrown open July 1 to more than 2 million federal and postal workers hired before 1984, few eligible employes walked through, agencies and departments report.

"We've had more action this week than in the previous six months," said Sally Marshall, personnel director at GSA. "Our transfers have been at 1 1/2 percent; we will probably end up about 2 percent."

Less than one percent -- 5,084 -- of the eligible Postal Service employes have switched. The service's total work force is 790,000.

At the Department of Health and Human Services -- a government leader in transfers -- the rate is about 3 percent. At Agriculture, the rate is 1.7 percent; at Interior, between one and 2 percent, and at Labor, 2 percent.

"A month or so ago, the figure was at 1 1/2 percent government-wide," said Jean Barber, associate director at OPM. "It will be 2 percent at the most. It's kind of a shame.

"I feel we did everything we could," she said of OPM's efforts to educate workers about the program. "Despite our greatest efforts, what you are seeing is people staying with what they know."

OPM produced or contracted for two separate videos and a voluminous FERS handbook, trained thousands of "decision advisers," distributed computer programs that employes could use to project pension income, and sent out a series of instructional bulletins.

"I believe if we had done more we might have been accused of overselling the system and people would conclude -- even more -- that if OPM is for this, it can't be good for me," Barber said.

"If anything, OPM did too good a job publicizing the program," said Edmund Hustead, senior vice president of Hay Huggins Co. "People began to be suspicious about why OPM wanted them to change."

But "inertia is the most important reason for the lack of interest," Hustead said. "I still say 40 percent of the people should transfer, but people don't always behave in economically rational ways.

"I have done a considerable amount of counseling and people sometimes get partial information that turns them off to considering the new system and nothing can change their minds -- if, for example, they think that OPM is trying to oversell it, or that Congress might cut back on the thrift plan benefits, or that Social Security is still in trouble. Just one of these type of perceptual things is enough to kill any chance of switching."

Dallas Salisbury, president of Employee Benefits Research Institute, disagrees. OPM's educational effort "on a scale of 1 to 10 would be about 1.5, compared with major corporations," he said. "They took a laissez faire attitude -- if people want to shift, fine, if they don't, fine."

Salisbury said that from the taxpayer's standpoint, the low transfer rate is a "double whammy."

"The new system is a good deal more generous than it would have been if it had not been for the desire to get the workers covered by {the old system} to switch," he said. "So now the taxpayers are paying for an old program that is very expensive and a new program that is almost as expensive in an effort to get people to join it."

But Cowan, a key Senate aide when Congress approved the new plan in June 1986, said, "Nothing was done to create transfers. The House really did not want to do it {allow transfers}, but Sen. {Ted} Stevens {R-Alaska} insisted" that longtime employes should have the opportunity to switch.

Cowan contends there are four reasons for the low transfer rate:Employe cynicism. "If the government is offering this now, it must be a bad deal for me. This is pervasive throughout the work force."

Complexity. "People get overwhelmed, and they say, 'This is ridiculous, I'm happy where I am.' "

Uncertainties. Congress held up some key changes until the last minute -- one provision prevented higher-paid employes from contributing more to the thrift plan on average than lower-paid employes could. This was eliminated shortly before Congress went home for Christmas.

Procrastination. "People waited until this month because decisions like this tend to be put off."

Anne Moss, deputy director of the Pension Rights Center, a nonprofit public interest group, said a decision to enter a retirement plan that relies heavily on personal savings requires financial sophistication, personal organization and work that "some people like to do and some people are just not into."

Moss noted that the new FERS plan reflects the "national shift to do-it-yourself retirement."

She said that while such plans may appeal to the high-income worker, many people are "just making it from paycheck to paycheck. Rather than subsidize savings through tax shelters, we would like to see basic pensions bolstered that would benefit all workers."

But with the new federal retirement system becoming much more like those used in business, all workers covered by FERS face a new series of decisions that will be reflected in the first pay period of 1988.

Until now, the 585,990 workers with savings accounts under FERS have had little choice in investments. Their $1 billion has been sitting in government securities. But starting next week, they can choose a bond fund or a common stock fund, investments with both a greater risk and a potentially greater payoff.