Former Prince George's County Executive Winfield M. Kelly Jr., who played a key role in a Miami-based company's successful campaign last month for a county cable television franchise, said yesterday he is considering running for the Maryland Senate.

The former Democratic executive said one of his reasons for running would be to defend the awarding of the cable franchise to his firm.

"There have been some attacks made against me, many of them of a personal nature," said Kelly, referring to criticism of his efforts as a spokesman and lobbyist for Storer Cable Communications.

The Prince George's County Council awarded the franchise for the northern section of the county to Storer last month, in the process rejecting the recommendations of an independent commission and an outside consultant hired to evaluate the cable proposals.

"Maybe my best forum to combat that is to meet them head on in the political way," he said. "It gives us a forum to bring our message to the people."

Kelly said he is considering a run for the seat presently held by Riverdale Democrat Thomas P. O'Reilly, a conservative, seven-year veteran of the Senate who has never been a Kelly intimate. Kelly is a resident of Hyattsville and what is now the 22nd District, but most of his area is slated to be incorporated into the 23rd as a result of reapportionment this winter.

Kelly said he intends to remain associated with Storer and will not run if company officials see a potential conflict with his role there.

"My involvement with Storer -- that's first," he said. "If some political trial would be out of the question, I wouldn't do it.

For his part, O'Reilly professed no great concern yesterday about facing Kelly. "I've heard rumors; there are always rumors going around. If Mr. Kelly wants to run, he's certainly entitled to," he said, then added several minutes later, "Has Winnie told you he's going to run? Hmmm. Maybe he will."

"It would be an interesting race," said Kelly, who lost his bid for reelection as county executive to Lawrence J. Hogan in 1978 and then vowed to fade quietly away into the world of private enterprise. By 1979, however, he became involved with Storer along with his former aide and Federal Commmunications Commission official John McAllister. Together the two spearheaded a controversial drive to win at least one of the county's cable franchises, an effort which culminated in the council's award to Storer in November.

Hogan, a Republican, vetoed the award, but the council narrowly overrode it after one council member was persuaded to change his vote. Within days, however, a group of dissident Democrats began gathering signatures to take the Storer award to referendum next fall, calling the award, in the words of one state delegate, "the sleaziest thing they've ever done."

Besides his own desire to "get out the truth" about Storer, Kelly said he is being urged to run by old Hyattsville supporters as well as his wife Barbara.