The youngest baby boomers turn 40 this year, leaving an entire generation not only in the throes of middle age but protected by federal law from age discrimination in the workplace. 

Despite the big demographic shift, there's been no explosion of age discrimination charges so far. The U.S. Equal Employment Opportunity Commission received an annual average of 19,500 age claims over the past two years, down slightly from 1992-93, and claims actually declined 4 percent in 2003 from a year earlier. 

But some experts think it may be only a matter of time before discrimination claims go up now that workers 40 or older comprise about half the nation's work force particularly with the age group now dominated by a generation known for going, and getting, its own way. 

''Since this generation is not shy about asserting their rights, I think you can expect to see an increase, maybe as people get into their 50s and 60s or in the next big economic downturn,'' said Joe Markowitz, a Los Angeles-based attorney who represents fired employees.
 
Thanks partly to medical advances and a growing life span, many boomers anticipate having the option to work longer at their jobs than previous generations did. If they want to be able to fund ambitious retirement plans, they may have little choice than to do so
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But what if their employers decide otherwise? 

The result can be a worker's worst nightmare: Getting replaced by a younger, cheaper employee. Proving age discrimination, however, has been difficult. 
Ron Harper says he planned to be an insurance agent with his company until he was 75. But he was only 48 when Allstate eliminated his job along with those of about 6,500 other agents more than 90 percent of them 40 or older. 

Following the layoffs in 2000, Northbrook, Ill.-based Allstate rehired the agents as independent contractors, a move that saved it $600 million a year. Harper, one of 29 agents who sued the company in 2001, contends Allstate took the action not only to save on retirement benefits but to evade employment laws. 

''In essence, what they did was they outsourced us,'' said the 52-year-old Harper, who now owns a pizza restaurant in Thomson, Ga., where he had worked for Allstate. ''They outsourced our jobs to ourselves. 

''Why'd they do it? They did it because we're 'old,' and because of those benefits.'' 

Allstate disputed that and so did a federal judge in Philadelphia. 

Judge John Fullam said last month Allstate had improperly required the agents to sign a release waiving their right to sue for discrimination in order to stay on as independent contractors, clearing the way for a trial. But he ruled that the company did not commit age discrimination because, even though the median age of those affected was 50, ''employees of all ages were treated alike.'' 

In another case, John Guz sued Bechtel National Inc. after being laid off at age 49, charging he was illegally fired in part because of his age. He had earned major promotions, merit raises and generally favorable job reviews in 22 years with the San Francisco-based engineering and construction company. 

But the California Supreme Court held in 2000 that older workers fired during staff reductions may not claim age discrimination simply because some younger employees were retained. 

Age discrimination is ''very difficult to prove right now,'' said Michael Lieder, a Washington-based attorney in the case against Allstate. ''Right now the burden is on the plaintiff for proving that the employer has some sort of stereotype that prompted them to take the action.'' 

A case that's to be argued before the U.S. Supreme Court in the fall, involving police officers in Jackson, Miss., could alter the legal landscape dramatically. The high court said this spring it would consider their appeal in order to clarify what older workers must prove in order to claim that employers were biased in favor of younger people. 

In the Jackson case, 30 officers and dispatchers sued over a pay plan they said gave bigger raises to workers under 40. A lower court ruled against them. 
''If the Supreme Court decides in favor of the employees, there's going to be a whole lot more cases go forward,'' said Bob Riordan, an Atlanta-based labor lawyer. 

In the meantime, companies that can cite valid business reasons for layoffs are on solid legal ground. 

''Employers have become more savvy about how to eliminate positions and restaff in the most 'economical' way,'' said Heather Sager, a San Francisco attorney who represents management in employment lawsuits. ''To that end, numbers save the day when an employer decides to eliminate an older worker's position and 'restructure' it into a job filled by a younger worker.'' 

Age discrimination in the workplace extends beyond layoffs, of course, but it's even harder to prove the existence of any age-related ''glass ceiling'' the invisible barrier that prevents employees from advancing any higher. 

Workplace consultant Connie Wang suspects many older professionals feel they're the victims of age discrimination but wouldn't challenge their employers because of an underlying concern that ''Who's going to hire me at my age?'' 
''We may have a much bigger problem than we can prove on paper,'' said Wang, managing director of CSW Global, a Connecticut-based consulting firm specializing in diversity issues. ''People may feel it, they may even be able to back it up, but they won't risk a formal claim.''