William Dean Christensen, a Montgomery County fugitive suspected of a dozen slayings in the United States and Canada, was convicted of third-degree murder yesterday for the 1982 stabbing death of a go-go dancer in Pennsylvania, where he already is serving a life term for a separate killing.

A Common Pleas Court jury in Scranton, Pa., deliberated for 12 hours over two days before returning the verdict against Christensen, 42, who has a history of sex offenses in Montgomery County. He was being sought by Montgomery police on a rape charge in July 1980 when he dropped from sight.

In the years since, according to law enforcement officials, Christensen has been convicted of rape in Montreal under an assumed name and has emerged as a suspect in killings in Canada, Pennsylvania, Maryland, New Jersey, New York, Georgia, Kentucky and Florida.

His only murder trials have been in Pennsylvania, however. He faces a prison term of 10 to 20 years in this latest case.

"We're not too pleased with the verdict. Obviously, the jury compromised from first-degree to third-degree," which is murder without premeditation, said Lackawanna County, Pa., District Attorney Ernest Preate Jr., who sought a first-degree murder conviction and said he wanted the death penalty for Christensen.

"But a conviction is a conviction," he said.

In September 1982, after serving one year of an 18-month sentence for the Montreal rape, Preate said, Christensen stabbed 23-year-old dancer Michele Angiers 30 times outside her apartment in Dickson City, a small working-class community in northeast Pennsylvania.

He remained at large until Dec. 4, 1983, when Philadelphia police found him sitting in a barroom, minutes after shooting to death 51-year-old Joseph Connelly outside another bar.

Christensen was sentenced to life in prison for the Connelly killing. His murder trial in Scranton began July 23.

There was no question that jurors would have convicted Christensen of first-degree murder and sentenced him to death had they known of his criminal history, said Daniel Preminger, his court-appointed lawyer. But the prosecution was not permitted to inform the jury of Christensen's record.

In Montgomery County, he was convicted in 1964 of stabbing a woman 19 times and served six months of a five-year sentence before being paroled against the advice of a psychiatrist. He was convicted of attempted rape in the county in 1972, but the verdict was overturned on appeal.

He later pleaded guilty to several charges stemming from the September 1972 sexual assault of a 21-year-old woman in Montgomery County and spent seven years in prison before being paroled April 1, 1980.

Three months later, a man matching his description raped another Montgomery County woman. Police obtained a warrant for Christensen's arrest, but were unable to find him.

After his release in Canada, he began a 21-month killing rampage, according to law enforcement officials in the states through which he allegedly drifted.