THE O.J. SIMPSON MURDER TRIAL : Blood Type Identifier Is Common : Forensics: If true, analysts say, contention that blood under Nicole Simpson’s fingernails differs from defendant’s and Goldman’s could mean someone else was at murder scene.

A protein identified in blood found under Nicole Brown Simpson’s fingernails and on her thigh is commonly used and accepted in forensic comparisons of blood samples. Barring a laboratory mistake, its identification--and its absence from her own blood and that of O.J. Simpson and Ronald Lyle Goldman--could indicate the presence of someone else at the scene when she and Goldman were murdered, experts said Thursday.

It also could mean that she inadvertently scratched one of her children or someone else earlier in the evening, they said.

“There are so many different possibilities, and we know so little about the actual results, that it is hard to speculate,” said Anthony Longetti, a professor of criminalistics at Cal State Los Angeles. “But if it is an actual result, and is shown to be accurate, then it has some significance” in determining the outcome of the case.

In his opening statement Wednesday, defense attorney Johnnie L. Cochran Jr. said the blood “came back type B in an EAP genetic marker.” EAP is scientific shorthand for erythrocyte acid phosphatase, an enzyme found in blood.

There are at least six readily identifiable forms of EAP, called A, B, C, BA, CB and CA. The blood from her thigh and under her fingernails was EAP type B, while she, Goldman and O.J. Simpson have a different EAP type--although Cochran did not say what their types are.

“It’s all very straightforward if you take everything at face value,” said one expert who asked to remain anonymous.

“That type (type B) is not possessed by any of the players. Therefore, that reveals that there is blood present from somebody else.”

“That certainly sounds like what you would call a pretty straightforward situation,” said molecular biologist Michael A. DeGuglielmo, director of forensic analysis for Genetic Design of Greensboro, N.C.

So far, the prosecution team has responded only that Cochran has taken a line from a laboratory report “out of context,” suggesting that the report has been misinterpreted. That also would not surprise DeGuglielmo. “That wouldn’t be the first time it has happened,” he said.