Despite mounting Democratic protests, Virginia conservatives yesterday claimed success in their controversial bid to raise money for television advertising this fall to sharply attack Democratic gubernatorial nominee Henry E. Howell.

"We couldn't be more pleased with the publicity," said David Keene, an Alexandria real estate salesman and one of the officials behind a fund-raising appeal last week that appeared under the congressional letterhead of Rep. J. Kenneth Robinson (R-Va.).

Based on two days' returns from the mailing, Keene said his group, "independent Virginians for Responsible Government," has already raised $18,000 and should clear "as much as $30,000" from the Robinson appeal. The group has admitted the letter is partly inaccurate.

That money will assure the group of producing what Howell has repeatedly said he fears the most in his campaign against Republican Lt. Gov. John N. Dalton: A strong anti-Howell television campaign in the final days of the race.

As officials of the Rosslyn-based National Conservative Political Action Committee, the sponsors of the mailing, were counting the receipts, another Democratic Party official was denouncing the Robinson letter as (ing) admitted factual errors and "prejudicial, inflamatory and contain gross distortions." That complaint came from Rep. Herbert E. Harris (D-Va.), chairman of the Democratic joint campaign committee, in a letter to Robinson.

Robinson could not be reached for comment yesterday, but the Associated Press quoted him as defending the letter at a Culpeper rally Saturday despite an admission that he did not check it carefully enough before allowing it to be sent. "I have no regrets," the AP said Robinson told a news conference. "I consider Henry Howell the most dangerous man ever to seek public office in Virginia."

In his letter to Robinson, Harris voted that one of the men connected to the fund drive was cited by the Senate Watergate committee for having performed "dirty tricks" for Richard Nixon's 1972 presidential re-election committee. "I cannot believe that you knowingly became involved with individuals having this kind of a political background," Harris wrote to Robinson.

According to the AP, Robinson said he was aware that Roger Stone, treasurer for the Independent Virginians, the group raising the funds was involved in the Watergate hearings. "I also knew he had been cleared of any wrongdoing and has since held office with the Young Republicans," Robinson was quoted as saying.

Dalton has disavowed any knowledge of the letter, calling it "very strong" Keene said his group has been in touch with Dalton's staff since the controversy broke and that Dalton's campaign had made no effort to discourage it from placing the planned advertising.

Sponsors of the letter have conceded that it incorrectly states Howell's position on school busing. Keene said Howell had created so much "confusion" over his position that the conservatives were dropping their plans for a television spot on the question.

Harris charged that Robinson "has brought the dark shadow of Watergate in Virginia" and urged his Republican colleague to disassociate himself from the letter.