Eugene A. Tafoya, the former Green Beret accused of attempting to assassinate a Libyan dissident here last year at the behest of the Libyan govenrment, took the stand late today in his own defense.

Tafoya's attorneys, who in opening arguments labeled their client a "forgotten patriot," guided him gingerly through his 23-year career in the Army, including a stint in the elite Special Forces.

Tafoya, the son of a major in the New Mexico state patrol, said he joined the Army at age 14 to fight in Korea. He served three tours of duty in Vietnam, winning numerous decorations. He was discharged in 1976.

Much of Tafoya's time on the witness stand was taken up with arguments between his attorneys and prosecutors over the admissibility of certain documents.

For example, prosecutors successfully barred the defense from presenting a portrait of Tafoya in his Special Forces uniform with his 18 medals.

The prosecution alleges that Tafoya was working for Edwin P. Wilson, a former CIA agent employed since 1976 by the Libyan government, as part of a plot to liquidate opponents of the regime of Col. Muammar Qaddafi.

Faisal Zagallai last week identified Tafoya as the man who came to his apartment on Oct. 14, 1980, under the pretext of interviewing him for a job. Tafoya attacked him, Zagallai testified, and shot him twice in the head, blinding him in one eye.

On Wednesday, Tafoya is to give his version of the incident. He is expected to claim that he went to Zagallai's apartment to deliver a message from the CIA.

Tafoya claims he received instructions from a CIA agent, who has not been identified, to warn Zagallai to stop activities "endangering detente between Egypt and Israel," according to Tafoya's attorneys. Tafoya is expected to testify that he shot Zagallai in self-defense after the Libyan pulled a gun on him.