A conservative organization about to launch a television advertising campaign against Virginia Democratic gubernatorial nominee Henry E. Howell agreed today to change the ads because Republican candidate John N. Dalton said they are inaccurate.

In a weekend letter, Dalton told the organization, the Independent Virginians for Responsible Government (IVRG) that it would be inaccurate to say, as one of the planned television spots do, "Howell claims to be opposed to unionization of our policemen, firemen and teachers."

Dalton said in his letter, "As a matter of fact every working person in America, including policemen, firemen and teachers, has the right to unionize, which neither Mr. Howell nor myself opposes. What Mr. Howell favors, and I oppose, is the extension of collective bargaining privileges to public sector unions."

John T. Dolan, chairman of the IVRG, said in a telephone interview that the ad to which Dalton objected is being changed. He said the assertion about unionization is being dropped and replaced by new language saying, "Howell has sponsored legislation to authorize collective bargaining by police and firefighters through unions."

Dolan said that assertion is based on Howell's co-sponsorhip in 1970 of a Virginia Senate bill that would have permitted collective bargaining by police officers and fire fighters in Virginia.

Dolan said that in the original sport the word "unionization" was used to mean "collective bargaining," and not the right to join a union. "I don't really agree with Mr. Dalton's conclusion that the original version was inaccurate," Dolan said, "but there is no point in quibbling over this. Howell's record is so objectionable as it is, we want to describe it in a very straight way."

In this campaign, his third try for the governorship, Howell has said he would not propose legislation permitting statewise collective bargaining by public employees. He has said, instead, that he favors a constitutional amendment giving cities and counties greater autonomy, including the right to decide whether they want to bargain with public employee unions.

During the Democratic primary campaign, Howell said that he as governor could establish collective bargaining for executive department employees of the state. His opponent, former Attorney General Andrew P. Miller, said that would be illegal since the Virginia Supreme Court has ruled that collective bargaining by public employees would require authorization by the General Assembly.

Dalton's letter to Dolan is the second objection by the Republican candidate or his staff to inaccuracies in statements made by the anti-Howell organization, which operates independently of the Dalton campaign organization.

When the IVRG was formed, it sent out a fund-raising letter signed by Rep. J. Kenneth Robinson (R.-Va.), alleging among other things that Howell had once advocated busing Northern Virginia school children to Washington schools.

In fact, Howell said in a 1972 television interview, "We can't afford to let the District of Columbia go to pot. If there's going to be some distribution of the young people of the District of Columbia into Maryland and Virginia to save our nation from being a divided black-white nation, then we've got to try this."

Dalton campaign manager William A. Royall disvowed the letter, citing its inaccuracy on the direction of the busing condoned by Howell. Dalton merely described the leter as "very strong." Robinson has stood by it, with the exception of the direction the school buses were supposed to travel.

The Fairfax County Fair Election Practices Commission was scheduled to meet tonight to hear a complaint against the IVRG letter filed by State Sen. Clive L. DuVal II (D. Fairfax). The findings of the commission have no legal standing.

The IVRG plans to begin its anti-Howell television sports later this week in Roanoke and Richmond. The first series of spots will run for 10 days and will be followed by another series in the same cities, Dolan said, if the organization reaches its $95,000 fund-raising goal.

Meanwhile, another group has revealed plans for a series of anti-Howell television commercials. Americans Against Union Control of Government State Political Fund, headquartered in Vienna, will be running commercials "probably on morning shows like A.M. America or the Today Show," according to the group's treasurer, Roman K. Rice III.

Rice said the "purpose of these ads is to acquaint the public with Mr. Howell's position on public sector collective bargaining. He is for it, while Mr. Dalton is against it. This has become a major issue in the campaign in Virginia," Rice said the group is a "citizen's lobby" that opposes public sector collective bargaining and "abuses of big union lobbies."

He said the group plans to spend about $5,000 on the advertising campaign, which the group already has collected in contributions. The commercials are being made by a Crystal City firm, Bishop and Bryant, run by Norman Bishop and Susan Bryant.

Bishop formerly was communications director of the Republican National Committee and has worked in previous Virginia Republican campaigns. Both he and Bryant have for short periods managed the campaign of Virginia Republican lieutenant gubernatorial candidate A. Joe Canada.

Meanwhile, Dalton himself campaigned in Petersburg where Gov. Mills E. Godwin made the first of 11 scheduled campaign appearances on his behalf.

Speaking to some 350 conservative Democrats from Virginia's Byrd-oriented Southside region, Godwin lashed out at Howell as "the darling of labor leaders" who he said would tax and spend Virginia into peril.

"How are you going to explain Henry Howell to the businessman of Europe, who have invested many hundreds of millions of dollars here in this state?" Godwin asked.

"How would you explain Henry Howell to the rest of the people in this country who have always looked to Virginia to produce responsible leaders with fiscal integrity?" the governor also asked.

Godwin said the greatest danger was that Howell would shatter the cherished predictability of Virginia's government, which, he said, leads businessmen to feel it's a safe place to invest their money.