Leading Virginia Democrats, dismayed that Andrew P. Miller will exclude populist Henry E. Howell from his Senate campaign, warned yesterday that Miller's decision could ruin Democratic chances to defeat Republican John W. Warner.

"I think it's very unfortunate," said State Sen. Clive L. Dugvall II of Fairfax, a longtime Howell ally. "We need to pull the party together. It would be a tragedy now if the more conservative side [of the party] seemed to reject the more progressive wing."

His comments were echoed by former state Del. Carrington Williams, a moderate conservative from Fairfax, who along with Du Val had challenged Miller this summer for the party's Senate nomination.

"Yes, it upsets me and I think its going to upset some other people," said Williams. "My phone started ringing this morning and I think its having an adverse impact."

Miller, in a decision announced by his campaign director, said Wednesday that Howell, the Democrat's candidate for governor last year, has been asked not to campaign for Miller this fall. Howell, the Miller official said, is too divisive a figure and would detract from Miller's campaign.

But yesterday Democratic Party leaders in the Norfolk and Northern Virginia areas were openly critical of Miller's action. State Del. Johnny S. Joannou, a Portsmouth Democrat, said Howell could be used to reverse "a lack of enthusiasm" that the Senate campaign has encountered in the Tidewater area.

"I say put Henry in the black churches in Tidewater and use him with the labor groups," Joannou, a Howell supporter, said citing Howell's strong support among blacks and union members. "There is no reason why we can't put the Democratic coalition together again. We just can't have another Republican victory."

Williams said one of the people who called him yesterday had supported Miller in his unsuccessful bd for the Democratic gubernatorial nomination against Howell last year. "This person told me that the people who are doing the hardest work to get volunteers for Miller now are old Howell supporters," William said. "I'm afraid this could affect them . . . It's a net loss. It's thrown us back. I just don't know to what yard line."

Fairfax County Democratic Party leader Emile Miller said she had received phone calls from concerned party workers, including a Howell supporter who had just completed a canvass of 1,000 homes in Springfield for Miller. "She was a little upset," Emile Miller said, "but she's going to wait and see before making any conclusions."

Howell and Miller are both scheduled to attend a party fund raiser at Du Val's McLean home on Sunday and Emile Miller said the vent is an opportunity to restore unity among Northern Virginia Democrats. "It's too early to tell what the impact is now," she said. "People are going to wait to see what Andy says on Sunday."

She added, "For the first time since I've been involved in the Democratic Party here, everyone on the Fairfax committee is united behind the party's candidate. When the convention was over, everyone go together and said, "Hey, this is it. We've all got to back Andy.' I wouldn't want to see anything spoil that."

Virginia Democrats have been crippled by a decade of dessension between the party's liberal and conservative wings. During that period, Virginia has been the only state in the nation that has failed to elect a Democratic governor or U.S. senator.

Miller has worked to win conservatives back to the party in his campaign against Republican Warner, and in doing so has shunned close association with his principal intraparty rival, Howell.

Howell offered to campaign actively for Miller, but Miller's staff director, Allan Clobridge, told Howell in a recent meeting that he would not be scheduled for any formal campaign appearances by the Miller campaign.

Yesterday, however, Clobridge said "We have not rebuffed Henry Howell. We have just defined his role as letting him do what he wants and we hope he will continue to speak favorably for Andy."

Clobridge said Lt. Gov. Charles S. Robb of McLean is the only state figure who is being scheduled to speak for Miller as an integral part of the Senate campaign. "We decided not to use surrogates because Andy is a strong state figure in his own right," Clobridge said. "Chuck ROBB IS THE ONLY right," Clobridge said. "Chuck Robb is the only wide Democratic elected official."

The dissatisfaction among Howell partisans in Norfolk and Northern Virginia could be crucial in the November election because Democrats historically depend on large margins in the Norfolk area to offset Republican votes in the Richmond suburbs, western Virginia and parts of Northern Virginia.

However, many campaign officials in the Hampton Roads area predicted in interviews this week that voter turnout there will be low this year. They say that a shortage of funds has kept campaign activities low and his prevented an effective voter registration drive in black neighborhoods.

Howell was elected lieutenant governors as an independent in 1971 and has made three unsuccessful races for governor. His populist proposals and outspoken advocacy of consumer protection and civil rights has built up a loyal following among black voters, organized labor and liberals - a hard core of support that enabled him to upset Miller last year in a gubernatorial primary.