WASHINGTON - The Supreme Court made it easier today for any worker over 40 to allege age discrimination, ruling that employers can be held liable even if they never intended any harm.

About 75 million people - roughly half the nation's work force - are covered by the decision. However, the ruling makes it clear that older workers will have a high threshold to prove their claims.

Justice John Paul Stevens wrote that in some cases employers are within their rights to treat workers differently because of age.

"Age ... not uncommonly has relevance to an individual's capacity to engage in certain types of employment," wrote Stevens, who at 84 is the court's oldest member.

The ruling sides with older police officers in Jackson, Miss., in saying they do not have to prove that the city deliberately tried to discriminate against them, just that the policies disproportionately harmed them. Nevertheless, the high court dismissed the suit, saying officers did not demonstrate that.

The ruling means that older workers now have less of a burden to raise their claim in court when suing under federal law, although ultimately it may still be hard for them to win.

The decision was unanimous in dismissing the police officers' suit, but 5-3 in holding that such suits are permitted under age-discrimination laws. Chief Justice William H. Rehnquist did not participate in the decision.

The Supreme Court already has said the so-called disparate impact claims are allowed under Title VII of the 1964 Civil Rights Act, which bans discrimination based on sex, religion or race. Today, justices said it should be no different for age discrimination, although it ruled the scope of liability is narrower.

At issue was workplace polices that appear neutral but actually disproportionately hurt older workers. Advocates for the aging say few employers would ever be up front about intentionally favoring younger workers, making age bias claims hard to win absent the rare "smoking gun."

But employers say allowing disparate impact claims under the Age Discrimination in Employment Act would hinder their ability to make necessary decisions based on age-neutral factors, such as training or performance, even if the impact happens to be greater on older workers.

The ruling in some ways strikes a compromise between the two.

On the one hand, it allows older workers to make a disparate impact claim under the ADEA regardless of intent; but at the same time, it permits an employer to cite "reasonable" factors, such as cost-cutting, to justify a practice that penalizes older workers so it prevails at trial.