The Justice Department decided not to seek appointment of an independent counsel to investigate Judge Douglas H. Ginsburg after concluding that his involvement or financial interest in 16 cable television matters while he was a high-ranking department official was too minimal to violate federal conflict-of-interest laws.

In a 116-page report dated Feb. 6 and released yesterday by the special three-judge court that appoints independent counsels, Assistant Attorney General William F. Weld said he found "no reasonable grounds to believe that further investigation or prosecution is warranted."

Ginsburg was nominated to the Supreme Court Oct. 29 after the defeat of Robert H. Bork and withdrew nine days later after admitting that he had smoked marijuana while a professor at Harvard Law School.

Media reports in the interim suggested a possible conflict between Ginsburg's handling of cable industry matters as head of the Justice Department's Antitrust Division and his investment of almost $140,000 in Rogers Cablesystems Inc., a Canadian company with U.S. operations.

Weld noted that "no evidence of venal conduct or self-dealing was even remotely suggested" by Ginsburg's participation in a Supreme Court case involving cable operators' First Amendment rights or in other matters.

More than 50 past and present government officials, including Ginsburg, were interviewed during the probe by FBI agents and lawyers from the department's criminal division. Weld, head of the criminal division, made the final recommendation because five higher-ranking department officials recused themselves from investigating their former colleague.

Weld's report suggested that Ginsburg's involvement in the Supreme Court case was less central than Ginsburg indicated on a Senate Judiciary Commmittee questionnaire when he was nominated to the federal appeals court here.

In a statement that sparked the first report, by The Associated Press, about a possible conflict, Ginsburg told the committee he was "a principal participant in determining the government's position . . . and supervised the drafting of our brief."

Weld found that Ginsburg's participation was "personal and substantial," as defined by federal conflict-of-interest law. But he said Solicitor General Charles Fried could recall only one conversation with Ginsburg about the case -- while checking his coat at a restaurant.

Although Ginsburg's deputy, Charles R. Rule, recalled Ginsburg reviewing and editing initial drafts of the government's brief, it was "rewritten in the office of the solicitor general; he does not recall any participation" by Ginsburg in the rewriting, the report states.

Federal law prohibits government officials from participating personally and substantially in any matters in which they know they have a financial interest. The report found that Ginsburg's involvement in the Supreme Court case was proper because the case had "no direct and predictable effect" on Rogers Cablesystems.

The report also found that:

Ginsburg had no financial interest in proposed Federal Communications Commission rules involving multiple ownership of cable systems.

His participation in proposed FCC rules involving "must-carry" regulations was "insubstantial, and proof that he had knowledge of having a financial interest . . . is lacking."

The other 13 cable matters did not warrant a preliminary investigation.