Democrat Henry E. Howell warned Virginia broadcasters last week that they have a legal obligation to cover him and others running for state office, advice that has now ensnarled his gubernatorial campaign in a bitter dispute with many station owners.

Barely a week after Howell mailed his advice - complete with legal footnotes - to each of the state's 131 broadcasters, he has been accused of a blatant attempt to force the stations to give him more free air time for his views.

Howell's letter was "an insulting attempt to intimidate broadcasters," the Virginia Association of Broadcasters has charged. ". . . No politician has the right to try and put pressure on the media," claimed Republican nominee for governor, John N. Dalton.

Howell defended the letter yesterday, saying he had hoped it would stimulate expanded coverage of the state's Nov. 3 general elections.

He was quoted by the Associated Press as telling station WHSV-TV in Harrisonburg that his only regret was in failing to send a similar letter to Virginia newspapers.

But he quickly said he still was considering that.

In his two-page letter to the broadcasters. Howell cited six court decisions on the industry's obligations to provide debate on public issues. The Federal Communications Commission, which regulates broadcasters, goes "so far as to consider how you meet this challenge in their licensing and construction-granting procedures," Howell said.

That sentence, coupled with the court cases and use of Howell's law office stationery, triggered much of the criticism. "It was an attempted exercise in prior restraint," complained Waynesboro broadcaster M. Robert Rogers, a professed Republican who was the first to complain publicly about the letter.

Denials of the charges by Howell and Frank Bolling, his press secretary who drafted the letter, have only intensified the issue as far as Rogers is concerned. Rogers said Bolling told him "part of the motivation" for the letter was Howell's fear that Dalton would soon mount a far more expensive broadcasting advertising campaign that Howell's financially pressed campaign will be able to afford.

The 30-year-old Bolling, who published a now-defunct Washington entertainment guide before joining Howell last spring, conceded that the campaign was concerned by the expected extent of Dalton's advertising, but said he had only "related" to Rogers that others were interpreting money as the motive for the letter."That was not the basis of the letter at all," Bolling said.

Howell probably was ill-advised to "go out dangling FCC rules at them (the broadcasters)" Bolling said. ". . . We just wanted to encourage them to participate" in the campaign.

In the letter, Howell told broadcasters the FCC requires them to "present fair and equal images" of the candidates. "However, I believe that responsibility to the public not only lies in your equal treatment, but also in your fullest treatment of the subject." He underlined the words "equal" and "fullest" in the letter.

In the past, Howell has not hesitated to criticize both print and broadcast journalists for what he has seen as shortcoming in their coverage of his two previous campaigns for governor.

After his narrow loss to Republican Gov. Mills E. Godwin in 1973, Howell threatened to sue the National Broadcasting Co. for $10 million for what he said was a false election-day characterization of him as advocate of school busing. He never filed the suit, although he claimed the remark on NBC's "Today" show cost him the election.

This year he attacked the Norfolkbased Landmark Communications Corp., which publishes daily newspapers in Norfolk and Roanoke and owns a Norfolk radio and television station, for failing to cover his campaign.

Bolling said yesterday, however, that Howell has "had excellent coverage" from the state's broadcasters and that his letter wasn't a complaint. "Quite frankly, they are limited in what they con do, as we are limited," Bolling said.

One of the few broadcasters to defend Howell yesterday was James Mays, news director of Landmark's WTAR-TV in Norfolk. "He is well within his rights to write a letter to whomever he wishes," Mays said. "I didn't take any offense at the letter."

Many others did. "I was a shock to me," said William Poole, president of WFLS in Fredericksburg and head of the broadcasters' group. Whatever Howell's intentions were in sending the letter, "it sure has backfired o them," he said.

Rogers, who said he has contributed $500 to State Sen. J. Marshall Coleman, a Republican running for attorney general against a Howell-supported Democrat, said the letter has "already inhibited us."