Anyone under the age of 55 need not apply. So says the charter of the Wave III Corporation in Alexandria, which plugged in its computer last Monday and began training 31 men and women in computer programming.

What makes this latest computer venture stand out is that it trains retirees from all walks of life--from truck drivers to career housewives to generals--in work that can be performed at their own pace and often in their own home, if they choose to lease or buy a home computer. And it is free.

"The whole thing got started on the premise that there is a shortage of programmers nationwide and there is a shortage of meaningful second careers for retired people," said William A. Haybyrne, Wave III's local managing director.

Fernando Lopez of Arlington was one of 31 area residents over age 55 who began the three-month training program, through which Wave III hopes to build up a stable of qualified computer programmers. After completing the course, students are obligated to program one short job each for the company, after which they are free to use their new skills as they wish.

Wave III officials, of course, hope the new programmers will elect to continue working for the company, programming at their own pace such things as municipal information systems and banking systems.

"I like to keep busy and supplement my income, and I am ready to learn something new," said Lopez, who retired from the Army in 1967.

The creator of the program is Eric Knudson, chairman of Wave III's parent company, ACS, who appeared last October as a witness before the House Select Committee on Aging. He testified at a hearing on older workers about Wave III's first venture, which opened in Bradenton, Fla., near Sarasota, a year ago.

At the hearing, Rep. Claude Pepper (D- Fla), who at 81 is the oldest member of Congress and chairman of the committee, said that ACS and Wave III "are in the forefront of this enlightened trend. . . . You have designed and implemented innovative personnel policies to maximize the potential of older workers."

The company expanded here, said Knudson, to "tap the burgeoning community of federal government retirees as well as to offer Wave III's programming services to the huge federal marketplace."

According to Knudson, the company can offer the free training--which costs about $3,500 per student--"because in New York we pay a $5,000 employment agency fee to find a qualified programmer." The Alexandria program is the second in a series of 10 he hopes to have opened around the country by 1984 to help ease what he calls the "acute" shortage of programmers.

Knudson says a lot of applicants "have difficulty in believing that this is for real and that we don't charge them. . . . Our benefit is that we teach them what we want them to know: our business. We are not teaching a general data processing course."

All that the participants owe the company at the end of training is completion of one contract (a 3- to 5-day effort), for which they are paid $90 a day. Knudson expects that two-thirds of the people who finish the class will end up working part time for Wave III. "Not too many companies will hire a 66-year-old programmer," he added. "But they are free to pick up and go."

After placing ads in local newspapers the company received over 1,000 applications for the Alexandria program, including one from a couple in Oregon who said they would move to the Washington area if they were accepted. After applications were screened, about 180 people took an aptitude test. From these, 60 were selected to participate in the first two classes (the second will begin in March.)

The first class consists of 28 men and three women, ranging in age from 55 to 68. Haybyrne said Wave III plans to conduct five classes this year. "That will give us about 150 programmers to work with," he said. The company will conduct future classes as the need for programmers arises.

"Ten years ago I retired from the military and wanted to do as little as possible," said John Andrews, 65, who will commute to the course from Fairfax County. "But this sounded very interesting." Andrews received information about Wave III from Alexandria's Retired Officers Association, which made part of its mailing list available to Wave III.

"We think this is an outstanding program," said Doug Carter, director of placement at the Retired Officers Assocciation, who had made several calls to Florida to inquire about Wave III's operation there. "Everyone spoke highly about it. . . . And we're very enthused about getting retired officers second careers. This program is really leading the way in the area."

Wanda Schobelock from Springfield, who's enrolled in the first class, also works part time in remedial reading. "This is something I can do and still be involved with the reading," said Schobelock, who at 55 just made the age cutoff for the program.

Knudson said he got the idea to call the new company Wave III from Alvin Toffler's book "The Third Wave," which forecasts the rise of a society characterized by smallness rather than bigness where more people will work at home at electronic cottage industries.

But the name Wave III conjured up different ideas to some senior citizens in Florida. "A couple of women in their late 60s stopped into our center in Bradenton, which is located in a shopping center, soon after it opened," said Knudson. "They said they had heard that Wave III was a big senior computer dating service. When I explained what we did, one of them replied, 'Well, you do have a lot of men around here, then.' "

Knudson tried to explain to her what Wave III actually did. But he admitted that, so far, applications and enrollments in the classes have been running 3 to 1 male.

When the woman heard this, she brightened up again. "Well," she said. "Can we come in and take a look around?"