For most of his career, Barry Levitt of Scranton, Pa., felt like nothing could stop him. With a Ph.D. from the Massachusetts Institute of Technology and a dream job as a communications research scientist, "I was given lots of responsibility, like giving presentations to get grants, and I felt very important," he says.

But somewhere around age 50, things started to change. While Dr. Levitt still wanted to excel on the job, younger workers started getting the plum assignments. "I started feeling like a dinosaur," he recalls. At 58, he retired.

Sound familiar? The pattern of the now 63-year-old Dr. Levitt's career is well known to many older Americans. Recent studies have found that about three-quarters of workers age 50-plus want to work beyond age 65 -- and that their motivation to work tends to increase with age. Yet older employees say that all too often their efforts go unrewarded.

According to the Center on Aging and Work/Workplace Flexibility at Boston College, the majority of workers age 50 and over who were surveyed in focus groups feel underappreciated and lack the respect they used to enjoy. Gail Golden, a management psychologist at RHR International consultants in Chicago, adds: "There's an underestimation of older workers that is rampant. There's this idea that they are slow and untrainable."

There's no evidence to support such ideas, however, says Helen Dennis, a specialist on aging, employment and retirement issues who was a delegate to the White House Conference on Aging last year. "What we have learned about aging and brain health is that people can grow intellectually beyond age 50. There's no reason to assume that people in midlife can't be profound contributors."

Employment specialists are taking a strong interest in the disconnect between older workers' motivation and their declining sense of usefulness because of what lies ahead in the U.S. labor market: The vanguard of the baby-boom generation is approaching retirement. If these millions of workers can't find more satisfaction or opportunity on the job -- if they can't get more training, appropriate raises or expanded roles -- the resulting brain drain could cripple productivity across many industries, says Bill Zinke, president of Human Resources Inc., a consulting firm in Boulder, Colo.

To date, most companies haven't addressed the challenge. That means older workers have to take the initiative to get what they want from the office, whether it be a promotion, more pay or respect. Here are a few steps that can help:

SPEAK UP. If you are in your late 50s or older, your boss could be making some big, and mistaken, assumptions about you and your plans for the future. He or she might think you're getting ready to retire, or you've reached a point in your career where you're satisfied with your role.

If that's not the case, speak up. Tell your manager that you have no plans to retire soon or that you would like to work, say, another eight to 10 years, if possible. Talk about your goals on the job. Perhaps you want to be promoted or manage a larger team. This way, you make it clear you haven't lost your ambition.

If you have concerns about the way your job is going, "it's up to you to tell your manager," says Beverly Kaye, founder and chief executive of Career Systems International, a consulting firm in Scranton that advises companies on how to recruit and retain employees.

Ms. Kaye suggests scheduling a meeting with your manager. And make clear in advance that you'd like to talk about your career, so your boss can be prepared. Go to the meeting equipped with ideas about improving your situation, whether it be taking on a new responsibility or getting more training in a certain area of your field.

TOOT YOUR HORN. Many older workers make the big mistake of assuming that their managers know how valuable they are. "You have to keep giving examples of your contributions," says Bob Gibson, president of Negotiation Resources, a consulting firm in San Francisco.

He suggests dropping an email or mentioning to your boss each time you have completed a project, reached a goal, solved a major problem or had some other kind of success. Even in your 50s and 60s, Mr. Gibson says, "keep planting the seeds. After a while you can translate that into more money, a promotion, more responsibility, or whatever it is you want."

BECOME MORE VALUABLE. Aside from trying to excel in your immediate position, aim to gain importance in other areas of your company in a way that only a mature worker can. For example, become a mentor for younger workers. Depending on your company, this may be a formal role assisting a particular young employee, or you can take it upon yourself to offer help informally to new talent.

Another way to add value: Assist in your company's recruiting efforts, either by conducting interviews or visiting college campuses to meet with job seekers.

WORK ON NEGOTIATING SKILLS. Older workers are more likely than younger workers to see their salaries plateau for the simple reason that they don't change jobs as often and so miss the opportunity to negotiate a bigger leap in pay when moving from one company to another.

You may, however, win bigger raises if you learn to negotiate more effectively. For one thing, be specific when you try to persuade your manager to approve a salary increase. "Don't say 'I'm a good manager' or 'I'm good with people,' " Mr. Gibson says. "Give precise examples of your achievements, such as, 'I have increased sales by 11%, and that translated into an increase in profits of X%.' "

If you feel you are underpaid, find out what similar positions are paying at other companies by checking job listings at job-search Web sites like Monster.com, Careerbuilder.com or Hotjobs.com.

Also, time your conversation. Talk to your boss about a raise six months before your annual review. Employees often wait until the review itself -- but by then raises are usually set.

BRAINSTORM WITH PEERS. If you are having a hard time dealing with some issues you believe are age-related, consider raising them with other older employees to see whether they share your concerns.

Issues may include that you're not getting the same training opportunities as your younger colleagues; that your suggestions to your boss for making your job more challenging are falling on deaf ears; and that you think you're perceived as having reached your potential even though you have a good decade of steam left.

"If you can't talk about these issues, you really can't solve them," says Marcie Pitt-Catsouphes, director of Boston College's Center on Aging and Work.

Come up with specific concerns and proposals for change and meet with a human-resources manager to discuss them, adds Ms. Kaye of Career Systems International.

STAY CONNECTED. No matter how old you are, make an effort to remain part of the mainstream on the job, Ms. Golden says. Relate to younger colleagues as peers, whether that means inquiring about their work, going to lunch together occasionally or asking for their expertise on a project.

"This doesn't mean you should pretend you're 22 years old," Ms. Golden says, "but spend time with younger workers and value what they bring to the table. If you don't show younger workers respect, you can't expect respect from them."

Also, guard against old-fogy-isms: "Don't fall into ways of speaking about the 'good old days' and how young people dress," Ms. Golden says. "And whatever you do, never, ever talk about your eye problems."