A U.S. District Court judge ruled yesterday that a female companion of master burglar Bernard C. Welch, the man convicted of the 1980 murder of physician Michael Halberstam, was Welch's "willing partner" and liable for $5.7 million in damages to Halberstam's widow and children.

In a written decision in a lawsuit brought by Halberstam's widow, Judge Aubrey E. Robinson said that Linda Sue Hamilton, Welch's companion for five years, "had guilty knowledge, and knowingly and willingly assisted in Welch's burglary enterprise." Hamilton was "vicariously liable" for Halberstam's murder in December 1980, Robinson said.

Hamilton was never charged in connection with any of Welch's activities.

Halberstam's widow, Elliott Jones, sued both Welch and Hamilton for $81 million in damages, saying that both were engaged in a "joint criminal venture" in the course of which Welch shot and killed Halberstam during a burglary of their Northwest Washington home.

Welch was convicted last April of the murder and sentenced to 143 years in federal prison. Hamilton was given limited immunity from prosecution and testified at Welch's trial.

It is unclear whether Jones will ever collect any of the money awarded yesterday. Hamilton has stated that all her and Welch's assets have been either spent or attached by creditors and the Internal Revenue Service. The IRS alone has filed a $24 million lien against those assets.

In an interview yesterday, Jones said she was "personally satisfied" by Robinson's ruling. "No one is going to get any money out of it, but this is nice," she said. "I feel like a final judgment has been given. I did not like that she was walking around unaccused all this time. I never had any doubt that she knew."

But Hamilton's lawyer, Albert J. Ahern, said that while Robinson's ruling was "popular," there was "absolutely no chance it will be sustained" on an appeal, which Ahern said he would file.

"There is no basis for what he Robinson did," Ahern said. "There was no evidence that she Hamilton had notice of violent activity" by Welch, Ahern said, adding that Welch could have been a "fence" for stolen goods "for all she knew."

During a hearing on the suit last January, Hamilton acknowledged receiving more than $1 million from Welch in 1978 and 1979, but said she believed him when he told her it came from his "investments" in stocks, real estate and coins.

Jones' lawyer, Jacob A. Stein, told Robinson it was "incredible" that Hamilton never questioned Welch about the source of the money.

Robinson agreed yesterday, saying that "Hamilton's explanations of her lack of knowledge are incredible" given that she acted as "banker, bookeeper, recordkeeper and secretary" for Welch, filing income tax returns and depositing large sums of money into her bank account from the sale of gold and silver bars but not withdrawing money to pay for the items that were being sold.

In response to Ahern's arguments that Hamilton was fooled by Welch, Robinson said that Hamilton "was compliant, but neither dumb nor duped."

Robinson concluded that Hamilton was aware that Welch was committing armed burglaries and that Halberstam's murder was a "natural and forseeable consequence of Welch's activities as a professional armed burglar."

Robinson awarded $91,000 in damages to Halberstam's sons, Charles and Eben, $123,000 to Jones and $5.5 million to Halberstam's estate. Jones is the personal representative of the estate.

Stein yesterday said that the Halberstam estate has a "very strong moral claim to any funds that are available." Financial compensation "has always been a secondary consideration" for Jones, he said, but she would "certainly look into" the possibility of collecting the $5.7 million Robinson awarded.

Hamilton's accountant has said that much of Hamilton's money was lost in speculative investments Welch made, and that the IRS took what was left.

In a recent interview, Hamilton said she was supporting Welch's and her three young children with money from her parents. She said she recently applied for public assistance in Great Falls, where she now rents a home, but was rejected.

A federal district court judge in Alexandria has ordered the sale of the couple's sprawling $1 million ranch home in Falls Church to pay liens from the IRS and other creditors. The house has been on the market since last July. Ahern said yesterday that the couple's other home, in Duluth, Minn., is being sold by a bank there that foreclosed on their mortgage.