ANNAPOLIS, DEC. 2 -- A Maryland appeals court today overturned the conviction of a Silver Spring man in an unusual rape case in which medical test evidence was presented linking the man's chromosomes to the woman's aborted fetus.

The Maryland Court of Special Appeals did not say that the test was wrong, but said that, so far, it had "not been accepted as reliable in the relevant scientific community." The court ordered a new trial for Kenneth Sylvester Cobey, 28, who was sentenced to four life terms and four 20-year sentences for the September 1985 attack on an Arlington woman in a Silver Spring park.

The 29-year-old woman became pregnant as a result of the rape and had an abortion the next month. Police sent samples from the aborted fetus to a genetics scientist in Oregon who was studying the use of chromosomes in determining parentage. The test results used by prosecutors in the case, like blood tests commonly used to test parentage in child support cases, could have proven that Cobey was not the father but could not have proven that he was.

The Oregon scientist testified during Cobey's two trials -- the first ended in a mistrial -- that her test could not exclude the possibility" that Cobey was the father.

The chromosome test used in the "Montgomery County case is different from the "genetic fingerprint" tests that have been successfully used recently in British and Dutch murder and rape cases. Supporters of those tests, which analyze the DNA portion of chromosomes containing an individual's specific genetic code, contend that they can positively identify individuals in the same way that fingerprints can. The test used in the Montgomery case, on the other hand, examined a different part of the chromosome known as heterochromatin.

The Montgomery County prosecutors, who were not available for comment on today's decision, did not depend entirely on the chromosome tests during the trial.

Thirteen days after the attack, Cobey was stopped by D.C. police as he was driving a car that was later identified as belonging to the victim. The victim testified that a pair of blue shorts found in the car was the same pair her attacker wore. She also said her assailant, for some reason, tore a book of matches in half and gave her one piece before leaving; a torn half of a similar matchbook was found in the car. Also, samples of semen and hair taken from the victim's body and clothing matched Cobey's, although they would not rule out other assailants.

Cobey said during his trial that he was the victim of mistaken identity. He said he had borrowed the victim's car from a friend named Mack, whose last name and address he said he did not know.