A federal jury in Chicago has convicted Washington lawyer Lee G. Lovett, a key figure in this area's cable television franchise wars, of mail fraud in a 1980 bribery case involving the former mayor of an Illinois resort community.

The jury, which deliberated for 18 hours, returned guilty verdicts Monday on two mail fraud counts involved in an alleged scheme to bribe the mayor of Fox Lake, Ill., in exchange for help in winning a cable franchise.

Lovett was acquitted on a single count of conspiracy to bribe and three counts of interstate travel in furtherance of bribery.

Lovett, 51, successfully represented applicants for cable franchises in the late 1970s and early 1980s in Alexandria and Arlington, Anne Arundel and Baltimore counties. His clients lost out to competitors in Fairfax and Prince George's counties and in Rockville.

Lovett's lawyer, Plato Cacheris, said yesterday that the conviction will be appealed. Lovett, who is free on bond, is scheduled for sentencing Oct. 3 in U.S. District Court in Chicago. He faces up to 10 years in prison and a $2,000 fine.

Lovett's office said he was in Chicago yesterday and unavailable for comment.

Federal prosecutors charged that Lovett offered Richard Hamm, then the mayor of Fox Lake, about 40 miles northwest of Chicago, a 5 percent interest in the franchise in exchange for Hamm's help in awarding the winning bid to Lovett's client, U.S. Cable of Hackensack, N.J.

Prosecution witnesses testified that the alleged secret arrangement was worth between $150,000 and $250,000 to Hamm.

Hamm also involved former Fox Lake Village Trustee Richard Gerretsen and an accountant, Kurtis Boore, in the alleged conspiracy, according to court testimony. All three men have pleaded guilty in the case and testified against Lovett under plea agreements with prosecutors.

Hamm, who lost a bid for reelection earlier this year, also has pleaded guilty to charges of taking bribes to secure liquor licenses and garbage and towing contracts for area businesses.

U.S. Cable won the Fox Lake franchise "totally independently," according to one prosecutor, because "the other five village board members thought they had the best presentation." Hamm nevertheless received the 5 percent payoff, according to prosecution testimony.

In the Washington area, Lovett was criticized by some cable operators, who complained that he promised more to local governments than the cable companies later were able to deliver. "We're still living down some of the promises he made," a former executive of Alexandria Cablevision Inc. said in a 1982 interview.

Other operators praised Lovett as a hard worker who got the job done.