Security at the U.S. Embassy in Moscow from mid-1984 to 1986 was bedeviled by confusion, laxity and back-biting among Marine guards, according to the first day of testimony in the court-martial of Marine Staff Sgt. Robert Stufflebeam at Quantico yesterday.

Reports of security infringements by Stufflebeam, on trial for fraternizing with Soviet women while guarding the embassy, were virtually ignored for almost two years before he was arrested, the court heard.

Andrew Colantonio, a former embassy security officer, told the jury of five officers and three enlisted men that he never followed up with an investigation after Stufflebeam voluntarily reported having had contacts with women the sergeant thought may have been Soviets or Italians.

When Stufflebeam reported early contacts with women, Colantonio admonished the Marine, but did not investigate further, he said under cross-examination by defense attorney James Bagley.

Last March, 20 months after he made his report to Colantonio, Stufflebeam was arrested on fraternization charges by the Naval Investigative Service (NIS) in connection with its sex-and-spying probe of Marine Sgt. Clayton J. Lonetree, convicted of espionage by a court-martial at the Quantico Marine Corps Base last month.

Stufflebeam, 25, of Bloomington, Ill., is charged with three counts of having had contact and sexual relations with Soviet citizens, of failing to report the contacts and of having lied about some contacts. The offenses carry a maximum of 14 1/2 years in prison.

According to a sworn statement by Stufflebeam, admitted into evidence yesterday, he first told investigators that he could not remember having had sex with two women and denied other contact with the Soviets. He later said that he had sex with Soviet women on three occasions in the summer and fall of 1985.

In other testimony, Stufflebeam's subordinate in Moscow, Cpl. Duane Parks, said he had reported Stufflebeam's fraternization with Soviet women to "the chain of command" in Moscow over a period of 18 months, but nothing happened "against Stufflebeam."

Documents entered into evidence show that Parks told probers that embassy security officer Fred Mecke discounted the allegations against Stufflebeam as being motivated by revenge.

Parks said he first reported Stufflebeam's July 1985 contact with two women three to four months after the fact, when Stufflebeam had reported him to superiors for two minor infringements of Marine rules. He believed Stufflebeam had framed him and he wanted to get even, he said.

Later, during the Lonetree investigation, Parks told NIS investigators about Stufflebeam's contacts with Soviets, court papers show.

In an earlier statement to agents, Parks described Stufflebeam as "vain, conceited, unreliable and rude . . . . I have no reason to believe he was involved in espionage, but I know he was oversexed."

Parks described security at the Moscow embassy as "extremely lax" and said other infringements included black marketeering.

Stufflebeam is accused of having lied in official statements about fraternization. Parks said under cross-examination that he himself had been discovered entertaining two Polish women in his room at the Marine barracks. Although "nothing happened" with them, Parks said, he had lied in a sworn statement about contacts with Eastern bloc women.

Parks said he recieved a "non-punitive letter" about the incident.

Earlier, a Marine guard's testimony directly contradicted that of Master Gunnery Sgt. Joey Wingate, head of the Moscow guard detachment, on the matter of which bars were off-limits to Marines.

Stufflebeam is charged with drinking at a bar he "knew to be off-limits."

Wingate said there was only one off-limits "dollar bar," where U.S. currency is used, in the Mehz hotel in Moscow.

But Sgt. Antoine Labadie, who had also served in Moscow, described four bars in the hotel as off-limits. He said there was not a clear understanding about which bars Marines could patronize.

In all, three witnesses gave three different versions of which bars were off-limits.