The Florida Supreme Court ruled yesterday that mentally competent adults have the right to refuse or to end life-sustaining medical treatment under certain circumstances.

The 6-to-0 ruling involved Abe Perlmutter, a retired New York City cab driver who had moved to Fort Lauderdale and who died more than a year ago after he insisted that doctors disconnect a respirator keeping him alive.

The court said Perlmutter had the right to disconnect the devices that kept him alive despite a terminal illness. However, the justices stressed their ruling was limited to nearly identical cases.

Perlmutter, 73, had amyotrophic lateral sclerosis, better known as Lou Gehrig's disease.

In Greenfield, Mass., a judge ordered an immediate end to dialysis treatments for a 78-year-old nursing home resident, despite testimony that the decision means almost certain death for the mentally incompetent, terminally ill man. The man's family said that if he could choose, he would want the costly treatments ended.

On Monday, the Massachusets Supreme Court reversed the state Court of Appeals, which had ruled that an incompetent patient's family and physicians could end extraordinary life-preserving treatment if they felt the patient would want it that way.

But the hig court reserved that power for judges and courts, and sent the case back with instructions to discontinue dialysis if Earle Spring's condition had not improved.

Witnesses at yesterday's hearing said Spring's condition had deteriorated slightly in the seven months since the first ruling in the case.

In Wilmington, Del., a man has petitioned a court to allow his 55-year-old wife, in a coma since a Dec. 6 automobile accident, to be taken off a life-support system. The case is expected to got to the state Supreme Court.