Both the Republican and Democratic nominees for governor of Virginia have agreed in principle to hold at least one televised debate this fall, spokesmen for the candidates said yesterday.

The debate between Republican Lt. Gov. John N. Dalton and Democrat Henry E. Howell would run between 90 minutes and two hours, and would be broadcast by five educational television stations in prime time, they said.

Confirmation of the debate plans, the first between gubernatorial candidates in Virginia since 1969 came after Howell, in a Norfolk press conference, publicly challenged Dalton to a series of televised debates. Later in Richmond, Dalton's manager, William A. Royall, sarcastically accused Howell of "talking when he should be listening," and said plans for at least one debate had been approved by Dalton.

The debate apparently will be held in September at the College of William and Mary in Williamsburg, in the same hall that served as the site for the third and final television debate between President Gerald Ford and Jimmy Carter last year, a Howell spokesman said.

Delighted by the reception of the presidental debate, the college's board of visitors last year offered the hall to the state's political parties for a gubernatorial debate. Howell said yesterday he would accept the offer "without qualification" and urged Dalton, a graduate of the Williamsburg college to debate him there "on his own home ground."

Royall said Dalton was anxious to debate Howell and believed the Williamsburg site would be acceptable.

Bruce Miller, director of news and public affairs for Central Virginia Educational Television, which operates stations in Northern Virginia and Richmond, said last night that the Northern Virginia station (Channel 53) was seeking debates among the nominees for lieutenant governor and attorney general as well.

The five stations that will broadcast the gubernatorial debate hope that the candidates will agree to a second debate, possibly in October in Charlottesville, Miller said.

Howell, who ran for governor as an independent four years ago, repeatedly tried to get Republican Mills E. Godwin to debate him on television, but Godwin refused.

Howell debated his Democratic primary opponent, Andrew P. Miller, frequently before the June 14 Democratic primary, but Miller, in what some Howell aides said was a mistake, agreed to only one televised debate.