Candidates in two Northern Virginia legislative races were accusedyesterday of violating laws in their campaigns for seats in the House of Delegates.

The Republican who is challenging state Del. Dorothy S. McDiarmid (D-Fairfax) in Tuesday's elections, accused the incumbent of violating state election laws by not properly identifying a mass-produced letter from Gov. Charles S. Robb as campaign literature.

In Arlington, county Democratic Party Chairwoman Charlene Bickford filed a criminal complaint against Charles G. Viars, a Republican legislative candidate, accusing him of violating the county's zoning ordinance by posting political signs.

Jeanne Morrison, the GOP candidate in Fairfax's 35th House District, said that she had asked Fairfax Commonwealth's Attorney Robert F. Horan and the Fairfax County Board of Elections to investigate what she called "illegally circulated unauthorized campaign material."

McDiarmid, Northern Virginia's senior Democratic legislator, denied any impropriety. She acknowledged that the letter did not include the required statement that it was authorized by her campaign committee.

"Yes, it could have been an oversight," she said. "But I don't think it is needed on a letter like that."

Morrison said she was "truly shocked" that "my opponent would attempt to deceive voters by having her campaign committee anonymously mail out a piece of unauthorized material disguised as official correspondence from the governor of the commonwealth."

George Stoddart, Robb's spokesman, said the Democratic governor wrote the letter to McDiarmid constituents "and would write 50 more on her behalf." In the letter Robb says that McDiarmid "is one of the few who has earned the respect of all the members of the General Assembly."

McDiarmid, who is in line to become chairman of the House Appropriations Committee if reelected, said Morrison has made several inaccurate remarks about her during the campaign. "I have not said anything, because she just doesn't know," said the legislator.

Neither Horan nor an election board official could be reached for comment.

Viars, who is running against Democratic Del. Warren G. Stambaugh, said the charge was ridiculous and denied he has placed any improper signs in the county.

As a result of a lawsuit Viars filed this fall over the county zoning ordinance, the county agreed to allow candidates to erect free-standing signs, no larger than 1 1/2-feet square in certain areas, according to Arlington County Attorney Charles G. Flinn.

Despite that agreement, Bickford said last night she has cited "many, many violations" by Viars in the past two months, including the erection of some signs as large as 4 feet by 4 feet.

Violation of the ordinance is a misdemeanor, Flinn said.