The sad fact is that many unemployed workers waiting for the jobs they lost because of bad times won't get those jobs back, even when the economy improves.

Their jobs--like the buggy-whip makers of the past--have become obsolete. And the world, says career consultant Ronald L. Krannich, has passed them by.

This "structural unemployment," the result of high technology and other changes in the economy, is a term currently in vogue, with President Reagan singling it out as the cause of the current high rate of joblessness.

Whatever the political arguments, change is escalating in today's work place, says Krannich; the savvy people will keep pace by constantly reassessing their careers. Whereas we once thought in terms of a lifetime career--and perhaps the same job--we now have entered an era where "15 jobs, five careers and many work lives" may not be unusual.

Workers "must continuously acquire new skills in order to adjust to job-market realities," says Krannich, who has written a guide, Re-Careering in Turbulent Times: Skills and Strategies for Success in Today's Job Market (Impact, 293 pages, $7.95). It is aimed at helping workers avoid job loss through structural unemployment.

Krannich, who heads Development Concepts Inc. of Manassas, himself abandoned a college teaching job when declining student enrollments reduced that profession's career possibilities.

"I believe we are in the midst of a profoundly revolutionary period," he says, "which will require individuals to re-career several times during their work lives. Like their buggy-whip maker and shoemaker counterparts of yesterday, the recent victims must acquire new skills and change careers in order to join the ranks of the gainfully employed."

Krannich anticipates "a very difficult job market" for the future. Among the new job-market realities: We are moving from an industrial-service economy "in the direction of high technology and communication. This high-tech society demands highly specialized and skilled workers.

"But these workers should not be overly specialized or too narrow in their perception of the future demand for their skills," since what is new today may be obsolete tomorrow.

What emerges, in Krannich's view, is the need for a new type of generalist-specialist "trained for today's technology, flexible enough to be retrained in tomorrow's technology and adaptive to new jobs and careers that will arise today and tomorrow."

Two basic strategies to protect against becoming an outdated worker involve keeping abreast of developing trends in your profession and signing up for retraining programs that keep you in demand.

Retraining may be available through government programs, from colleges and vocational schools or from your employer. Krannich, however, cautions against assuming such programs will be provided, should your job be in jeopardy. The individual, he maintains, must take the initiative in maintaining his or her skill level, or run the risk of getting help that is too little and too late. "Few people have valid excuses for not acquiring the education and training necessary to function effectively in the job market."

One last recommendation: "Make an effort to learn one new skill each year; the skill can be related to work, family, community, or a hobby such as building bookcases, operating different computer-software packages, repairing appliances or remodeling your home." It will prepare you, says Krannich, "for making the career transitions necessary for functioning effectively in turbulent times."

Ronald L. Krannich is offering a free re-careering seminar May 16 from 7 to 9 p.m. at Hecht's, Tysons Corner. For information, contact Hecht's public relations, 626-8414. Back-to-School: Adults make up almost half of the full- and part-time enrollment in American colleges today, reports the College Entrance Examination Board. In a recent survey of 2,000 over-25 learners, 56 percent said it was because of a career transition.

The board has just published a helpful guide to workers pondering how to pay for new training they initiate on their own: Paying for Your Education: A Guide for Adult Learners (The College Board, 151 pages, $7.95).

"Unlike young college students who may be financially dependent on their families," says the board, "most adults . . . are self-supporting, and many of them have dependents of their own. They would like to enroll in degree and nondegree programs, but hold back because they are worried about costs.

"What adult learners often do not know is they can qualify for and receive financial aid. Your chances are still good for some aid (if only a loan), even if your yearly income is about $15,000, or if you did not do well in school when you were younger."

Along with listing sources of adult educational aid, including special funds for women and minorities, the book also details various programs aimed at shortening the time (and cost) of getting a degree.

The guide is available at book stores or from College Board Publications, Dept. E 94, Box 886, New York City 10101.