Three black slaying victims that prosecutors are trying to link to murder suspect Wayne B. Williams showed similar stab wounds, including a pattern of wounds on one body that could have been part of a ritual, a medical examiner testified today.

Dr. Joseph L. Burton, the medical examiner for suburban DeKalb County, said a pattern of two vertical stab wounds and five surrounding skin pricks on the abdomen of William Barrett, 17, "suggest a type of marking of the body or a type of ritual with the body."

Burton said Barrett was probably stabbed shortly after he died or while he was being strangled, which could indicate a type of ritual.

Barrett's body was found near the main interstate highway running east from downtown Atlanta just after midnight on May 12, 1981. His case is the only one in which prosecutors suggested that any kind of ritual killing might be involved.

Burton said Barrett's wounds looked "very much like" six stab wounds in the chest and abdomen that killed John Harold Porter, 28, in April, 1981.

He said Barrett's wounds showed some similarity to two superficial post-mortem stab wounds on the body of Eric Middlebrooks, 14, who died from a "blunt trauma" to the head in May, 1980.

Barrett, Porter and Middlebrooks are among 10 cases that prosecutors have been allowed to introduce into Williams' trial on two murder charges as possible evidence of a pattern of killings.

Prosecutors contend that fibers found on the bodies of the 10 victims match fibers found in Williams' house and cars, but such evidence has not been introduced. Williams is charged with the slayings of Nathaniel Cater, 27, and Jimmy Ray Payne, 21.

Barrett's aunt and cousin testified that Barrett visited his aunt's house one afternoon late in 1980 with two friends, one of which they later identified as Williams.

James Barrett, 23, and his mother, Mary Harris, testified that they never were able to identify the other man who was with Williams and William Barrett that day. They said they identified Williams in a police photo line-up only after his picture was featured in television reports about his arrest.

Eleven witnesses have testified that they saw Williams with six of the 12 young blacks whom prosecutors contend he killed during a 22-month period. Witnesses also have placed Williams at the funerals of three victims whose cases were investigated by a special police task force and at the scene where one body was discovered.

The Fulton County assistant district attorney, Jack Mallard, asked Dr. John Feegel, an associate county medical examiner, if Middlebrooks could have died "from being slapped upside the head with a slapjack?"

Feegel said a slapjack, or blackjack, a leather sack filled with shot, ball bearings or other metal, could have killed Middlebrooks. Police found a slapjack concealed in a ceiling when they searched Williams' house on June 22, the day after his arrest.

The prosecution also kept the door open today for later suggestions of a sexual motive in the killings.

Medical examiner Burton told lead defense attorney Alvin Binder he found no traces of sperm or rectal injuries on the three victims' bodies he examined. But, under Mallard's questionning, Burton later said he could not rule out sexual contact before the victims' deaths.