A Fairfax County Circuit Court judge yesterday dismissed cocaine distribution charges against an Annandale man, accepting a defense argument that the government failed to prove that the kind of cocaine sold was illegal under Virginia law.

Judge Barnard F. Jennings dismissed three counts of cocaine distribution against Richard Gobeille, 28, who was arrested last May and accused of selling about $15,000 worth of cocaine to police undercover agents. Gobeille could have been sentences to up to 40 years in prison on each charge if convicted.

The judge accepted the dismissal motion of defense lawyers who argued that the prosecution had failed to prove scientifically that the cocaine Gobeille allegedly sold was an illegal substance. There are two kinds of cocaine, one of which is made from coca leaves, which is illegal under Virginia and federal laws, and one made synthetically, which is rare and is simply not mentioned by the law.

Assistant Commonwealth's Attorney John T. Graham said he disagreed with the judge's decision, asserting that prosecution testimony proved the cocaine involved was illegal "within the realm of reasonable medical certainty." Graham said the probability that the cocaine is synthetic "is infinitessimally small."

Howard McClain, chief of the regulatory control division of the federal Drug Enforcement Agency, said yesterday he is not aware of the existence of any synthetic cocaine in the United States.

McClain said synthetic cocaine which is expensive and difficult to make, is not produced because of the cheaper and more readily available supplies of cocaine made from coca leaves.

According to prosecutor Graham, the state's chemist in the case, Jay Seigel of the Northern Virginia Consolidated Crime Laboratory, conducted routine tests on the cocaine obtained from Gobeille. The tests, Graham said, did not conclusively prove the substance was organizally derived cocaine. But since synthetic cocaine is unavilable, Graham said, the only reasonable conclusion from the test is that the cocaine tested is illegal.

Defense attorneys John K. Zwerling and Jonathan Shapiro of Alexandria said that the "probability" that the substance involved was illegal cocaine was not sufficient for conviction in a criminal case.

McClain of DEA said that it is relatively easy for any chemist to distinguish between organiz and synthetic cocaine, but that the tests necessary to make the distinction are not "routine" in criminal cases.

Even if the cocaine that Gobeille allegedly sold is found to be organic, and therefore, illegal, Gobeille cannot be prosecuted again for selling it, according to prosecutor Graham.

Defense attorney Shapiro said yesterday that other defense attorneys in cocaine cases across the country have tried to get judges and juries to see the distinction between illegal and legal cocaine. Shapiro said that as far as he knows, yesterday's case was the first time that a judge saw the distinction.

Prosecutor Graham said Judge Jennings' decision is not binding on other Circuit Court judges in Virginia and that the decision should not be seen as "carte blanche" for would-be cocaine dealers.

But Graham said the decision is "certainly going to make the law (against cocaine distribution and use) less persuasive than in the past."