Because many dead persons whose brains are not functioning are being kept breathing by hospitals, a presidential commission yesterday urged Congress and every state to adopt an up-to-date definition of death.

The aim, said commission members, is to help doctors and families "turn off the machines" -- and eliminate the possibility that a person may be legally alive in one state and dead in another.

Meeting an Airlie House in Warrenton, Va., the commission voted unanimously to ask Congress (for federal jurisdictions) and states to define death as either heart and lung shutdown, the classic legal definition, or "irrevocable cessation of all functions of the entire brain, including the brain stem."

The problem is urgent because 23 states and the District of Columbia still cling to an ancient definition that recognizes only heart stoppage. In the 27 states (including Maryland and Virginia) that recognize brain death, some statutes are vauge or confusing, Alexander Capron, commission execution director, said.

This means doctors and hospital officials often fear legal action if they remove life supports from a brain-dead person whose heart is still beating because of the artificial supporters. Families are sometimes rebuffed by judges when they try to have supports removed.

No one knows how many people are brain-dead but being kept breathing on artificial respirators, but the number may be significant. The commision examined two months' records from four unidentified hospitals that treat many trauma cases. "At each we find five to seven cases that met our definition of death," said Renie Schapior of the commission staff. About half had been declared brain-dead, but the other half were being sustained until their hearts stopped -- usually within a few days for adults but often much longer for children.

The situation varied greatly among the hospitals. At one, artificial respiration was halted in all appropriate cases; at another, in none. "And this was in states both with and without brain-death statutes," Schapino said. t

Brain-dead people on machines "are not people being 'kept alive,'" said Capron, a law professor on leave from the University of Pennsylvania. "They are people who have expired whose hearts and lungs are kept working, through the function of the brains isn't there.

"When there is no clear definition, the physician faces a difficult choice. There are the old vital signs of life: a heartbeat, a heaving chest, a warm skin. But he knows that if he weren't giving respiration, there would be a corpse."

Yesterday's recommendation was the commission's first completed action. Formally known as the President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research, the group has created by Congress in November 1978 and started work in January 1980 with Morris B. Albram, former president of Brandeis University, as chairman.

The American Bar Association, the American Medical Association and the National Conference of Commissions on Uniform State Laws have approved the new definition of death after working with the commission.

The definition says that not only the upper or "higher" brain, which controls reason and though, must be dead, but also the "lower" brain or brain stem, which controls breathing. Some medical and academic witnesses urged the commission to call a person dead if only the upper brain is dead, but the commission rejected that as too "radical" a change.

This means that Karen Ann Quinlan -- still alive in a New Jersey nursing home after five years in a coma -- could not be declared legally dead. Her functioning brain stem keeps her breathing.

New Jersey -- as well as states such as New York, Pennsylvania, Massachusetts and Wisconsin -- has never adopted a brain-death statute.

Statute -- some clearer than others but few fully meeting the new standard -- have been adopted in Alabama, Alaska, Arkansas, California, Colorado, Connecticut, Florida, Georgia, Hawaii, Idaho, Illinois, Iowa, Kansas, Louisiana, Maryland, Michigan, Montana, Nevada, New Mexicao, North Carolina, Oklahoma, Oregon, Tennessee, Texas, Virginia, West Virginia and Wyoming.