Washington ? Rules that determine which workers are entitled to overtime pay could change drastically under new federal regulations proposed Thursday, the first update in more than 50 years.

Nearly 22 million Americans could be affected by new definitions of white- and blue-collar workers.

About 1.3 million lower-wage workers now exempt from overtime pay for working more than 40 hours a week would be required to receive it or a salary increase. But at least 644,000 well-paid, professional employees, such as some engineers, pharmacists and insurance claims adjusters, would lose theirs in the Labor Department’s proposal, which was submitted Thursday for a 90-day public comment period.

Millions of other workers would gain and lose under the new regulations, though their status isn’t clear. Industries most affected by the changes would be construction, retail, health care, business services and personal services.

Overtime pay is just one area of the nation’s labor laws that the Bush administration is tackling at the urging of business groups. The Family Medical Leave Act, job training programs and unemployment insurance also could be overhauled.

Employers have been pushing for changes in overtime pay regulations because of mounting lawsuits. Workers filed 79 federal collective-action lawsuits seeking overtime pay in 2001, surpassing for the first time class-action job discrimination suits against employers, according to the American Bar Assn.

Businesses and labor unions agree that the regulations, based on the 1938 Fair Labor Standards Act and last updated in 1948, are confusing. But they disagree about how to update standards that determine what jobs must receive an hourly wage of time-and-a-half for working more than 40 hours a week. Almost 110 million workers are covered by the law, about 80 percent of the work force.