State Del. Owen B. Pickett's withdrawal from Virginia's U.S. Senate race yesterday assures a free-wheeling and chaotic Democratic party nominating convention in June.

"It's going to be a donnybrook," said state Sen. Richard L. Saslaw (D-Fairfax). "There's going to be a mad scramble for delegates."

With a month left before the June 4-5 gathering in Roanoke, state Democrats find themselves with more than 3,000 elected delegates--and no declared senate candidates. Delegates say that is likely to mean a mind-boggling month of telephone calls and visits by hopeful candidates.

"Anything can happen, and is probably likely to," said Del. Warren G. Stambaugh (D-Arlington). "It's time for somebody to grab the old bull by the horns, get on the phone and start calling delegates. It's a golden opportunity for somebody."

Adding to the confusion is the fact that state Democrats have yet to fill some 374--or more than 10 percent--of the convention's 3,624 delegate seats. Because the nomination of Pickett, a Virginia Beach delegate, had until recently seemed a foregone conclusion, local party officials had difficulty convincing anyone except the most devoted party regulars to serve as delegates.

But that indifference vanished yesterday as Democrats started calling local party officials in hopes of winning the open delegate seats. "I would think we wouldn't have any trouble filling out our numbers," said Fairfax Democratic Chairman Dottie Schick, whose county is almost 40 delegates short of its 392-delegate goal. "That's called understatement."

Under party rules, the delegates who were chosen at local mass meetings around the state last month will select those to fill the empty delegate slots. That effectively puts a valuable bargaining chip in the hands of local party chairmen and party regulars in areas where many delegate vacancies are reported--areas such as Arlington, which failed to fill 42 percent of its 119 delegate seats, and Alexandria, which left 22 percent of its seats vacant.

Sharon Davis, Arlington's party chairman, said yesterday that she has not yet figured out how to fill the vacancies. "They're not clear on how to work it," she said of state party officials, "and they kind of threw the ball to me."

The expected combat among candidate's for the party's nomination has some Democrats glowing with anticipation. "I think it sounds like a lot of fun," said Stambaugh, who had been planning to pass up the convention for his 20-year high school class reunion. "Maybe I should go. It sounds like it's going to be real exciting."