Former Virginia Gov. Mark Warner (D) will make an announcement Thursday regarding his future political plans, a senior adviser said Tuesday, and Democratic Party insiders widely expect that he’ll enter the race to replace retiring Sen. John Warner (R).

Warner’s entry would instantly transform the race into a major pickup opportunity for Senate Democrats.

Although his name has been floated as a viable vice presidential prospect in 2008, Warner has said in recent public appearances that he’s been mulling either the Senate bid or another gubernatorial run in 2009.

Eleven years ago, Warner, a successful businessman who co-founded the Nextel telecommunications firm, spent about $10 million of his own money on a losing campaign against John Warner.

A Thursday announcement by Warner for the Senate seat would kick off an already busy weekend for Old Dominion Democrats. The steering committee of the Democratic Party of Virginia is scheduled to meet in Fredericksburg on Friday, and Warner has his annual pig roast, an event that can become a who’s who of state Democrats, for Saturday.

If, as expected, the popular former governor enters the Senate race Thursday, he will sail through the Democratic primary without any serious competition and would face the winner of an all-but-certain GOP battle between Rep. Tom Davis and former Gov. Jim Gilmore.

According to a one-day Rasmussen poll of 500 likely voters conducted on Sept. 5, Warner begins with an advantage over both would-be Republican opponents.

In a race with Gilmore, the automated poll found Warner leading 54 percent to 34 percent. The poll showed Warner leading Davis 57 percent to 30 percent.

Warner also had a better favorable to unfavorable rating than both Republicans.

Warner was viewed favorably by 68 percent of those surveyed and unfavorably by 28 percent.

Gilmore’s favorable to unfavorable rating was 49 percent to 42 percent, and Davis’ was 43 percent to 35 percent with 22 percent not knowing enough about him to have an opinion, according to the poll.