WASHINGTON (AP) _ Republican presidential candidate Pat Buchanan is preparing to bolt his party and begin a quest for the Reform Party nomination Oct. 25, officials close to the conservative commentator said Wednesday.

Two officials, speaking on condition of anonymity, said Buchanan was planning to announce his departure from the GOP in suburban Washington, New Hampshire and perhaps other key states.

The officials cautioned that Buchanan could still reverse course and stay out of the increasingly fractious third-party bid. But they said he intends to bolt, and the departure was virtually certain.

In the clearest signal yet of his intentions, Buchanan's campaign mailed hundreds invitations to supporters Tuesday night inviting them to a ``major announcement'' Oct. 25 at a Falls Church, Va., hotel, the officials said. As many as 3,000 invitations also were being sent for a New Hampshire stop, they said.

``He's almost too far down the pike to get out now,'' said one of the officials.

However, spokeswoman Joanne Hansen said no final decision has been made.

Lagging in GOP polls, Buchanan says he believes the party's nomination battle is rigged in favor of Texas Gov. George W. Bush, who he says is too moderate.

The Reform Party nominee would lay claim to almost $13 million in federal matching money. Party founder Ross Perot earned 19 percent of the vote in 1992 and 8 percent in 1996.

Republicans fear that a third-party run by Buchanan would siphon conservative votes from their nominee. He won the New Hampshire primary in 1996 and put a scare into then-President George Bush in the 1992 primaries.

Buchanan, however, would not be assured the nomination. A parade of celebrities and politicians are mentioned as potential candidates, including New York tycoon Donald Trump, Minnesota Gov. Jesse Ventura, former Connecticut Gov. Lowell Weicker, actress Cybill Shepherd, actor Warren Beatty and Perot himself.

A new CNN/USA Today/Gallup Poll shows limited support for the third-party alternatives. Buchanan had the backing of 9 percent of those surveyed in a three-way matchup with Bush and Vice President Al Gore, the Democratic front-runner. Trump had 10 percent in a similar three-way matchup.

The unfavorability ratings of Buchanan, Ventura and Trump have increased as speculation about their presidential bids drew more media attention.

Trump formed an exploratory committee last week, and says he would spend $30 million if he jumps in the race. Buchanan, who has had trouble raising money in the GOP race, could not match that total but has more political experience than Trump. He is said to be worried about Trump's financial resources.

The contest is already heated.

Trump consultant Roger Stone said Buchanan wants attention, not the White House.

``Pat's avocation at this point is running for president. It's all he does,'' Stone said in a telephone interview. ``Trump will spend $30 million to get on the ballots in every state. I don't think Pat can do it.''

Trump himself has called Buchanan's views ``prehistoric.'' Buchanan is a staunch, anti-abortion conservative who drew criticism for questioning whether Nazi Germany was a threat to America.

Ventura, the party's highest ranking elected official, has ruled out a 2000 presidential campaign, though the speculation continues. He is urging Trump to seek the nomination, saying Buchanan is too conservative on social issues for the party.

Buchanan is drawing support from the Perot wing of the party.

``I say to Roger Stone, `Bring your candidate on.' It'll be another head on the wall,'' said Pat Choate, Perot's 1996 running mate. ``I believe Pat is going to get in the race, win the nomination and, with any luck, the White House.''

Perot himself has not taken sides in the nomination fight and has not ruled out jumping in the fray himself.

The officials close to Buchanan say his meetings with advisers are filled with strategic and thematic discussions about the third-party bid. His sister and top adviser, Bay Buchanan, is exploring party rules and is already seeking to plant Buchanan backers in state party leadership posts. Buchanan and his advisers are discussing language Buchanan would use to explain his departure, though he has not yet formally begun writing the speech.