Before Elsie K. Perlmutter retired from her D.C. government job last year she took a number of steps to make sure the switch from office to home was a smooth one.

For one thing, she forewarned her two sons, those "big fat" holiday gift checks "will be scaled down."

For another, she did not want to slip into idleness. Instead she set about, at 69, to realize her "dream" of teaching others how to plan for retirement -- which, in part, meant going back to college.

As an instructor in management techniques at the D.C. Department of Human Resources, she had become aware of the keen interest city employes showed in a series of retirement seminars she initiated. "It was my hobby. There's a thirst for this kind of information. You may not be interested in pre-menstrual syndrome or male menopause, but you ought to be interested in retirement. It's everybody's concern."

Her motto: Failure to plan for retirement" means planning for failure." Instead, "If you do something about it -- if you do a little bit of planning -- you'll have a smoother transition. And there'll be more options open to you."

Too many people, she says, put off thinking about their later years because to them it means life's end. "Retirement," she counters, "is a time when you can realize your dream. Retirement won't go away. You'll be there."

As a trainer in the frequent series of retirement workshops offered by the Graduate School of the Department of Agriculture, Perlmutter advises on how to better meet the financial, psychological, social and health challenges retirees face.

Without some foresight, she cautions, one day you could be "a big shot in the government and then suddenly nothing," a hard adjustment for many to make. Husbands who have been managers "come home to begin to manage the wife. You can see how well that goes over."

You could run into trouble also if your social circle is "narrow," she says, or your life revolves around your job. Make "one good friend on the outside," she says, someone with whom "you can air your feelings. Your network of friends is an important resource.""

The current debate over Social Security, coupled with concern over inflation's continuing erosion of fixed pensions, says Perlmutter, has increased public awareness of the potential financial hazards of retirement, even among those for whom it is decades away. People want to know how they can prepare themselves adequately for a comfortable later life.

As early as age 40, "you better get concerned," she says. "The more you focus on it [retirement] the better position you'll be in to do what you want when you retire. Give yourself a head start." For example, since Social Security and a pension may not be adequate, "start to invest a little bit." When you are younger, "time works for you, which it doesn't in later years. You can take risks, which you can't later."

Retirement counselors suggest you will need about 70 percent of your current income to keep up your life style after you leave work. Your investments, however, will have to keep up with inflation if your pension has no cost-of-living increases. As Action for Independent Maturity (AIM), a retirement counseling organization, points out:

A couple who retired in 1970 on a comfortable but fixed income of $15,000 would need $31.700 in 1980 to maintain the same standard of living."

From her experience, says Perlmutter, "your expenses go down at first. There are no lunches. You're watching your money." But after that, "You say the hell with it, and your expenses begin to creep up until they settle down two or so years later."

Because of fears over retirement costs, the trend in past years toward early retirement (at 55 or 60) seems, says Albert E. Peterson, AIM's public affairs coordinator, "to be changing toward later retirement," to age 70 or older. Influencing this is the fact that "people are living longer, they're in better health and they want to stay alive."

(His Washington-based, 460,000-member organization, a division of the American Association of Retired Persons, is directed at pre-retirement workers.)

Peterson's view is backed by the Work in American Institute of Scarsdale, N.Y., which concluded in an 18-month policy study:

"For many people, the American Dream of spending their retirement years on the beaches or golf courses of the Sun Belt may be a thing of the past as increasing numbers of older people go back to work or postpone their retirement."

Adds Peterson: "An increasing number feel that giving up work completely is not the healthiest thing to do. Keeping active is definitely a good thing." Many firms, he says, are permitting retired workers to come back on a part-time basis or under flex-time or job-sharing arrangements.

AIM, formed in 1971, is one of a number of groups offering retirement-planning counseling to corporation employes throughout the country. Dun's Review magazine cites it as "the newest employe benefit." Giant Foods, Riggs National Bank and Washington Gas are among local firms subscribing to AIM programs.

Perlmutter believes quite strongly in working after retirement, either to supplement income or as a volunteer. "I'm not denigrating sitting on a beach, but that can't last."

List all the things you are good at, she says. "Then list all the things you'd like to do. Then brainstorm and begin to narrow down your list."

If you need more schooling, get going before your boss gives you that farewell handshake. Perlmutter's husband Samuel, for 30 years a government chemist, took qualifying courses to become a high-school teacher before he retired at 55. Now 71, he continued to teach at Winston Churchill High School in Potomac.

Many people fear poor health in their retirement5 years. "Hey," they tell Perlmutter, "I don't want to be decrepit and broken down.What can I do?"

Begin now, she says, "to get yourself in good trim." Pay attention to nutrition and get some exercise. You not only feel better, chances are your medical costs will be less. Perlmutter swims a half mile every day.

Where you are going to live also needs some advance planning."A lot of people," says AIM's Peterson, "have a desire to go off to the Sun Belt -- some place away from here. If you have those impulses, go stay there" for a time to make sure it's really what you want. "Subscribe to the paper. Talk to people. Make an intelligent market survey."

If you're a couple living in a large house, "you might consider moving to a smaller place. Or you could take in roomers. There are various alternatives."

No matter what goals you finally decide on, he says, "we urge that the spouse be included." At one workshop, he recalls, a man spoke up to say, "I'm thinking of moving to New Mexico."

"You never told me that," his wife retorted. "No way." She was not going to give up her friends and her church.

Doesn't Perlmutter miss some of that idle time those still job-bound day-dream about?

"I'm doing what I want to do. You can call that having time for yourself. I don't have idle time.

"I worked hard to get to this age -- and I want it known that I'm still working."