One-third of Virginia's Democratic state senators have "for varying reasons" declined to publicly endorse Henry E. Howell, their party's nominee for governor, Senate leaders acknowledged yesterday.

The lack of unity over Howell's candidacy contrasts sharply with the unanimous endorsement the senators are expected to deliver today to Charles S. (Chuck) Robb of McLean, their party's nominee for lieutenant governor, "I guess it's because he (Robb) is sort of seen as in the moderate tradition, like me," said Senate Majority Leader Adelard L. Brault (D-Fairfax) last night.

Missing from the list of senators endorsing Howell were several Richmond-area conservatives, but also absent from the list were three members of the senate who two years ago supported ousting the chamber's conservative leadership. All of Northern Virginia's seven Democratic senators including Brault signed the Howell endorsement.

"I don't think that it's surprising," Brault said of the senators' refusal to endorse Howell. "For varying reason they prefer not to be identified with the (Democratic) Rainbow ticket," Brault said.

However, he added that he was "satisfied that all 34 (senators) will vote for the Rainbow ticket," so called because those on it - Howell for governor, Robb for lieutenant governor and Edward E. Lane for attorney general - cover a spectrum of ideology from the moderate-liberal Howell to the conservative Lane. Among the senators whose names were missing from the Howell statement were Elliott S. Schewell of Lynchburg, William B. Hopkins of Roanoke, and Elmo G. Cross of Hanover all of whom supported a 1976 takeover the Senate's leadership.

The split seems to illustrate Howell's difficulty in securing the support of Democratic conservatives, including those who backed the losing candidacy of formre attorney general Andrew P. Miller, whom Howell upset in the June 14 Democratic primary. One of those absent from the Howell statement was William F. Parkerson of Richmond, who served as a co chairman of Miller's third congressional district campaign and another was Edward E. Willey of Richmond, president pro temport of the senate.

Howell's staff viewed the endorsement of the 24 senators as a plus for Howell in his fight Republican Lt. Gov. John N. Dalton. The senators who refused to sign the statement "certainly were the old-line ones who were in the Byrd organization," said Howell press secretary Frank Bolling.

After listening to the endorsement in Richmond Howell came to Northern Virginia, where his candidacy received the support of the Rev. Albert L. Hill, president of the Virginia State Baptist Convention, a group of predominantly black churches said to have 51,000 members.

In prepared remarks, Howell was more optimistic about his chances for defeating Dalton than he had been over the weekend campaigning in Norfolk.

"Everywhere I've gone in recent days the people are telling me. 'Henry, our time has come.'" Howell said. "There is nervousness in the board rooms of the big banks at the top levels of Vepco (Virginia Electric and Power Co.) because a people's victory in the making," Howell said.

As Dalton campaigned in Lynchburg yesterday, a group of conservatives announced in Richmond they were forming a group known as "Virginians for Dalton, Robb and Lane" to work against Howell but for the other two members of the Democratic ticket. The group is headed by former Democratic Rep. Watkins M. Abbitt of Appomatox ane former Democratic lieutenant governor Fred G. Pollard of Richmond.