Standing on the staircase of his 169-year-old McLean mansion, Clive L. DuVal, long regarded as one of Virginia's most conscientous and liberal state legislators, announced yesterday he was running for the U.S. Senate. His audience: two newspaper reporters, two television crews (one from an educational channel) and a handful of bleary-eyed supporters munching doughnuts.

Six hours later, in a tiny room of an Alexandria Holiday Inn, John W. Warner, a man who has never run for public office and is something of a novice in Virginia politics, did the same. His audience: at least four television networks, crews from all but two of Washington's five commercial stations, and a roomful of admirers.

The different audiences were dramatic testimony to the drawing power of a man DuVal and other Virginia Democrats have taken to calling "Mr. Elizabeth Taylor." Yesterday, perhaps more than ever, it was the 50-year-old Warner, a former Navy secretary, who was clearly basking in the glory of being the sixth husband of the 46-year-old actress.

She has, Warner said yesterday, "brought a new dimension to the role of a political wife." Last year she traveled across the state, drawing crowds of thousands in small Virginia towns where Republicans once could almost have held their meetings in telephone booths.

At one gathering alone at Warner's hilltop estate near Middleburg, the Warners raised $45,000 for Republican Gov. elect John N. Dalton's campaign. Throughout it all, Miss Taylor has proved a magnet for both public attention and national media coverage of the Dalton campaign.

Yesterday it was Warner's turn. Clapping his hands at her in Alexandria, Warner called: "Come on, Liz, today's the day." The large crowd of poshly attired middle-aged women burst into applause.

The Warners' political debut, although extraordinarily attractive to the press, left some of the state's more staid Republicans amazed.

In Richmond, asked why she supported ratification of the Equal Rights Amendment to the U.S. Constitution when her husband did not, Miss Taylor said: "Well, I've been working since I was 10. I have supported my family, a couple of husbands, I feel absolutely equal. I already feel I have equal rights. I feel women who are less fortunate than I have been may need this help. . . . I am for it."

Warner, who faces three other challengers for the Republican nomination to succeed retiring U.S. Sen. William L. Scott, also broke the traditional rules for playing the role of the willing but humble public servant. Asked to describe his standing in the race, Warner shot back at a reporter: ". . . I'm going to leave that up to you. That's what you're paid to do . . . The only message you have to carry out of here is that you're looking at a winner."

While many Virginia Republicans might have smiled at such a statement a year ago, no one is laughing at Warner now. His travels last year (20,000 miles by his estimate) raised huge sums for Dalton and scores of other local Repulican office seekers. That translates into political IOU's that Warner's staff hopes can be translated into votes at the GOP's June convention, which will name a candidate for Scott's seat.

Thanks to the impact of his wife, some top Republican Party officials are saying privately that Warner probably has slipped into second place in the race, ahead of his old college classmate and former Virginia Gov. Linwood Houton. That would still place him behind former national GOP co-chairman Richard Obenshain of Richmond, but ahead of State Sen. Nathan Miller of Harrisonburg. Warner yesterday would only say he is in - third place, coming on rapidly."

Both Warner and DuVal, 64, are among the wealthiest men in the crowded Virginia Senate race. Each is a millionaire. Their wealth may be crucial to financing their races, staffers for both men said yesterday.

Like Warner, DuVal, a state senator and a longtime consumer champion in the legislature, is probably better known by the company he keeps than by his political accomplishments. Long a supporter of Democrat Henry E. Howell, DuVal was Howell's Northern Virginia coordinator in last year's Democratic primary in which Howell defeated former Attorney General Andrew P. Miller - who also is a candidate for Scott's seat.

DuVal said yesterday he believes his ties to Howell would be an asset in the field of seven Democrat candidates, four of whom are from Northern Virginia. Other prominent Democrats disagree. "If it's not enough to stop him in the primary, it certainly will in the general election," State Senate Majority Leader Adelard L. Bcault of Fairfax said recently.

The way DuVal envisioned his chances at the Democrats planned state convention no one will win on the first ballot. But as other Nothern Virginians drop, DuVal said he expects to pick up their votes on subsequent ballots.

Also in the Democratic race besides Miller of Richmond are State Sen. Hunter B. Andrews of Hampton. Flora Crater of Falls Church, Del. Carrinton Williams of Fairfax, former Fairfax, Supervisor Rufus Phillips and Frederick Babson, a former Fairfax County Board chairman.

Neither DuVal nor Warner delved into substantive issues during their Northern Virginia announcements. DuVal portrayed himself as a "realist," but hedged when asked his view of the proposed Panama Canal treaty, which has become an issue in the crowded race. Warner has previously said he opposes the treaty.