The Rev. Ralph David Abernathy, who suffered a minor stroke last Friday, will receive a relatively new form of surgery, a brain "bypass" operation, to help prevent future strokes, surgeon Mel H. Epstein said yesterday.

A spokesman for Johns Hopkins Hospital said at a news conference that Abernathy, president emeritus of the Southern Christian Leadership Conference (SCLC), is expected to recover from the effects of the stroke, possibly without any permanent loss of speech, although he suffers from some slurring of words.

The surgery, scheduled for March 9 at Hopkins, is intended to prevent a second and probably fatal or totally debilitating stroke. In Abernathy's brain the artery that is 90 percent clogged by a buildup of plaque is the major artery leading up to the left side of the brain.

Epstein said that it is only a matter of time--possibly days or weeks--before this important artery is shut off completely unless further measures are taken. The result would likely be death or total paralysis and loss of speech and understanding.

Abernathy, 57, suffered a minor stroke at his Atlanta home Friday. Apparently a blood clot from the clogged artery broke loose and traveled to a branch artery in the area of the brain associated with speech. The clot blocked blood flow, starved the cells of oxygen and caused some damage to the brain.

Abernathy is in good spirits, and left the hospital yesterday to rest at home until the surgery next month, according to hospital staff member Diane McMahon. Abernathy was the president of the SCLC from 1968 to 1977, and is pastor of the Hunter Road Baptist Church in Atlanta.

The surgery Abernathy will receive has been performed on several thousand patients over the past decade, but is still experimental, because no information exists on its long-term effectiveness.

The principle of the surgery is to reroute blood around the clogged main artery, increasing the blood flow to the brain's left side.

Epstein said yesterday that surgery to clean plaque out of the major artery has proved too dangerous. Epstein said he will locate and sever the linguale artery in the scalp. He will then open an inch-wide hole in the skull, and sew the open end of the scalp artery to an artery on the surface of the brain. The place where the two arteries join is only centimeters beyond the blockage.

Thus, fresh blood will flow through the scalp artery directly into some of the major branches of the now-choked middle cerebral artery. The functions of the rerouted scalp artery will be taken over by other scalp blood vessels.

During the year after the operation, the scalp artery will stretch to a much greater size to accommodate its new job of carrying blood to major branches of the brain's circulatory system, Epstein said.

He said that eventually it could become almost as large as the middle cerebral artery that it will bypass. In addition, he said, if the cerebral artery should finally become completely blocked, blood from the new connection will actually reverse its flow and flood back toward the clogged artery and the branches it is supposed to serve, thus taking over its function.

The surgery is carried out under a microscope, as the arteries being sewn together are only about one-twentieth of an inch across. The surgery takes about 3 1/2 hours.

Hospital spokesmen said that Abernathy's memory and understanding are not impaired, but that he has some difficulty in putting his thoughts into speech. He can walk, and doctors said his recovery from the minor stroke has begun.