The Supreme Court significantly curtailed the scope of a federal law designed to protect disabled workers from discrimination yesterday. By a 7 to 2 vote, the justices ruled that the Americans With Disabilities Act does not cover people whose disabilities can be sufficiently corrected with medicine, eyeglasses or other measures.

In their broadest look at the ADA to date, the justices decided four disabilities cases, the most important being a pair of rulings that would prevent millions of people from seeking coverage under the landmark 1990 law. The highly anticipated rulings could profoundly affect individuals with a range of impairments -- from diabetes and hypertension to severe nearsightedness and hearing loss -- who are able to function in society with the help of medicines or aids but whose impairments may still make employers consider them ineligible for certain jobs.

"These decisions create the absurd result of a person being disabled enough to be fired from a job, but not disabled enough to challenge the firing," asserted Georgetown University law professor Chai Feldblum, who helped draft the statute and who was one of several advocates who said they would ask Congress to change the law.

The rulings represent a substantial win for employers, who praised the court's decision to limit those covered by the statute. "Employers make reasonable accommodations for employees who are truly disabled," said Steve Bokat, general counsel at the U.S. Chamber of Commerce, "but they should not have to relax necessary standards for employees who have common and easily correctable ailments."

The disability cases were closely followed by workers, businesses, civil rights advocates and the Clinton administration, which had urged the justices to interpret the law in a broad manner.

By identical votes of 7 to 2 in a pair of cases -- one involving two nearsighted pilots and the other a mechanic with high blood pressure -- the court ruled that when judges assess whether a worker pressing a disability-bias suit qualifies as "disabled" under the law, they must take into account any measures that lessen the worker's impairment.

By a unanimous vote in Albertson's v. Kirkingburg, the justices ruled that employers who set job qualifications based on federal safety standards are not required to dispense with those standards when a worker -- in this case, a truck driver blind in one eye -- obtains a waiver from the federal agency.

By a 6 to 3 vote, the court ruled that states must place certain mentally disabled people in community homes rather than hospitals. In a case focused on a provision of the ADA that prohibits discrimination by public entities, the court generally sided with two Georgia women with mental illnesses who had sued state officials for keeping them in a psychiatric hospital long after their doctors said they were ready to live in a community residence.

Enacted after years of effort, the Americans With Disabilities Act was meant to open jobs and public spaces to the nation's then-estimated 43 million disabled people. The law defines a "disability" as a "physical or mental impairment that substantially limits one or more . . . major life activities." Yesterday, the court addressed the most fundamental question of how to determine who is and is not "disabled."

The main ruling dealt with twin sisters from Spokane, Karen Sutton and Kimberly Hinton, who were turned down for pilot jobs at United Air Lines because of their extreme nearsightedness, failing the airline's minimum requirement for uncorrected visual acuity of 20/100. When they sued under the ADA, judges said the law did not cover people who can correct their disabilities -- in this case, with glasses -- and get along as well as most other people.

Yesterday, the Supreme Court agreed, rejecting the position of the U.S. Equal Employment Opportunity Commission and the majority of federal appeals courts.

"Looking at the act as a whole," Justice Sandra Day O'Connor wrote for the majority, "it is apparent that if a person is taking measures to correct for, or mitigate, a physical or mental impairment, the effects of those measures -- both positive and negative -- must be taken into account when judging whether that person is `substantially limited' in a major life activity." She said the language of the law requires a person to be limited "presently -- not potentially or hypothetically."

O'Connor noted that Congress had written in the law that "some 43 million Americans have one or more physical or mental disabilities" and argued that if the law were intended to cover all those with common, correctable impairments such as nearsightedness, that figure would have been far larger.

But the majority also emphasized that whether a person has a disability is an individual question and that some people who have prosthetic limbs or other corrective devices could still be considered "disabled" because of a substantial limitation of their life activities.

O'Connor was joined by Chief Justice William H. Rehnquist and Justices Antonin Scalia, Anthony M. Kennedy, David H. Souter, Clarence Thomas and Ruth Bader Ginsburg in Sutton v. United Air Lines, as well as in the related ruling involving a mechanic with hypertension, Murphy v. United Parcel Service.

Dissenting in both cases were Justices John Paul Stevens and Stephen G. Breyer. In a statement written by Stevens, they said, "[T]o be faithful to the remedial purpose of the Act, we should give it a generous, rather than a miserly, construction."

Roy C. Englert Jr., who represented United, said he was pleased with the court's ruling, which was cheered by other employers as well. Human resources lawyer Ted Gies said the court provided important "clarification" about who is covered by the ADA and its decision will help to reduce ADA lawsuits. "Most people would say," Gies said, "that the biggest human resource and legal challenge is the ADA."

But Michael A. Greene, a lawyer for the American Diabetes Association, said the ruling puts people who take medicine to function in society in a difficult position. "You're damned if you don't medicate, but you're damned if you do, because you lose your legal rights," Greene said, adding that sometimes impaired persons who can do the job might nonetheless seek special accommodations or extra time off for medical care.

The case on community placement, Olmstead v. L.C., spoke to increased efforts to move mentally ill people from institutions into communities in an effort to end their isolation. A key provision of the ADA says disabled persons shall not be discriminated against "by reason of their disability" by a government program or service, and the Justice Department has said that means programs must be offered "in the most integrated setting appropriate to the needs" of people with disabilities.

Georgia officials, backed by numerous other state and local governments, had argued that a state does not discriminate under the ADA when it keeps the mentally ill in hospitals, even though a community setting might be more desirable.

But in an opinion by Ginsburg, the court ruled that it is indeed illegal discrimination "when the state's treatment professionals have determined that community placement is appropriate, the transfer from institutional care to less restrictive setting is not opposed by the affected individual, and the placement can be reasonably accommodated, taking into account the resources available to the state."

Concurring justices stressed that states should have "wide discretion in adopting its own systems of cost analysis."

Dissenting were Rehnquist, Scalia and Thomas. In a statement for the trio, Thomas said it is not "discrimination" when mentally ill people are temporarily excluded from community placement centers.

Staff writer Kirsten Downey Grimsley contributed to this report.

The ADA Cases

* Sutton v. United Air Lines

Twin sisters Karen Sutton and Kimberly Hinton of Spokane, Wash., wanted to be United pilots but were rejected because they are nearsighted. The sisters had 20-20 vision with corrective lenses, but United requires uncorrected vision of 20-100.

* Kirkingburg v. Albertson's

Hallie Kirkingburg, a truck driver from Portland, was fired by the Albertson's supermarket chain after he failed a vision test. He was unable to meet vision requirements for commercial drivers, even with corrective lenses.

* Murphy v. United Postal Service

Vaughn Murphy, a mechanic from Topeka, was fired by the UPS because of high blood pressure he has had since he was 10. Murphy's physician said he was unable to lower his blood pressure below the Transportation Department-required level without serious side effects.

* Olmstead v. L.C.

Elaine Wilson, who is mildly retarded and has a borderline personality disorder, and Lois Curtis, who is mildly retarded and was diagnosed as schizophrenic, sued Georgia to get out of a state mental hospital in Atlanta and into community-based care.

Defining Disabilities

From 1992 to 1998, there were 108,939 complaints filed with the Equal Employment Opportunity Commission under the the Americans with Disabilities Act.

Impairments most often cited (as a percentage of all cases)

Back 16.7%

Emotional/psychiatric 13.7%

Neurological 10.8%

Extremities 9.6%

Heart 4.0%

Diabetes 3.6%

Substance abuse 3.0%

Hearing 2.8%

Blood disorders 2.6%

Vision 2.5%

Cancer 2.4%

Asthma 1.7%

SOURCE: Equal Employment Opportunity Commission

CAPTION: Plaintiff Vaughn Murphy at his Kansas home in April. Murphy is a mechanic with hypertension who sued United Parcel Service after being fired.