PHILADELPHIA — A federal judge yesterday barred the government from allowing companies to provide younger retirees with better health-care benefits than they give older ones who qualify for Medicare.

The AARP, an advocacy group for people 50 and older and the nation's largest advocacy group for retirees, sued in February to block the proposed rule change, saying giving differing packages to the young and the old amounts to age discrimination.

In her finding in favor of the AARP, U.S. District Judge Anita Brody said the U.S. Equal Employment Opportunity Commission (EEOC) lacked the power to make the change.

Brody said the proposed regulation also would violate a legal precedent that companies may offer different health plans to retirees of different ages only if the plans are of equal value or provide equal benefits.

EEOC Chairwoman Cari Dominguez said she planned to appeal.

The EEOC had proposed exempting retiree health plans from age-discrimination rules as part of an attempt to slow the trend of companies eliminating retiree health benefits.

The percentage of companies with more than 1,000 workers offering health coverage to retirees dropped from 80 percent in 1991 to 57 percent in 2003, according to a study by the benefits consulting firm Hewitt Associates and the Henry J. Kaiser Family Foundation.

Large employers and some unions have argued that age-discrimination rules are worsening the problem for people looking to retire before age 65, when they would qualify for free or low-cost care through Medicare.

Between 10 million and 15 million retirees receive health-care coverage from former employers. Of those, 3 million to 4 million are younger than 65.

Many companies offer a type of bridge health insurance for retirees in their late 50s and early 60s who aren't old enough to qualify for government health programs and likely would find it difficult to pay for medical care themselves.

It is also common for the same companies to provide a less-comprehensive package, or nothing at all, to workers once they turn 65 and qualify for Medicare.

American Benefits Council President James Klein said companies increasingly see their prime responsibility as providing coverage for the younger group. "Those are the people who need it more," Klein said.

"Absent an employer-sponsored plan, those people would potentially have nothing, and they might have to postpone their retirement if not for our help."

The AARP rejects that argument.

"You can't just arbitrarily decide that the oldest, frailest people will have their benefits reduced so that the less old can get a better package," AARP lawyer Michele Pollak said.