DENVER — Former Republican Rep. Bob Barr was nominated yesterday as the Libertarian Party's candidate for the U.S. presidency, defeating a crowded field in a raucous convention vote that went to six ballots.
Mr. Barr, a conservative standard-bearer who switched to the Libertarian Party less than two years ago, defeated Mary Ruwart, a biophysicist and longtime party activist, by 54 percent to 46 percent in the final ballot. Delegates late last night agreed that Wayne Allyn Root, a celebrity sports handicapper, would be Mr. Barr's running mate.
The party's 600 delegates eliminated the other eight registered candidates in earlier balloting over the course of six hours at the Libertarian Party National Convention, held here at the Sheraton Hotel.
The four-term congressman from Georgia vowed to run a high-profile campaign on behalf of the nation's third-largest political party, which espouses greater social and economic liberty.
"This team, this candidate, will not let you down," Mr. Barr told conventioneers minutes after his nomination. "This will be a historic, positive campaign that will succeed."
He dismissed any thought of running a symbolic campaign.
"We are not in this race to make a point, although a point will be made. We are not in this race to send a message, although a message will be sent," said Mr. Barr. "This is a campaign that will win, but we need your help to do so."
Mr. Barr, 59, became the most recognizable Libertarian presidential candidate in decades. He built a conservative reputation in Congress, gaining a national reputation for his advocacy of the impeachment of President Clinton.
He was defeated in the 2002 Republican primary after the state's redistricting plan combined his district with that of another incumbent Republican. He quit the party in 2006 over what he called its bloated spending and its scaling back of civil liberties after the Sept. 11, 2001, attacks.
During his campaign for the Libertarian nomination, Mr. Barr came under fire for some of his congressional votes, notably his early support of the USA Patriot Act and the Defense of Marriage Act, which defines marriage as a legal union between one man and one woman.
In his acceptance speech yesterday, Mr. Barr apologized for those votes. He criticized the Patriot Act for what he saw as its intrusions on personal freedom, and vowed to work for the repeal of the Defense of Marriage Act.
Third-party candidates have played pivotal roles in two of the past four presidential races. Republicans fear that a Barr candidacy could siphon votes from Sen. John McCain of Arizona, the party's presumptive presidential nominee.
"We're having this conversation because the last two presidential elections have been so incredibly close — one or two states, a few thousand votes, made the difference," said Denver pollster Floyd Ciruli.
He pointed to Green Party presidential candidate Ralph Nader, whom Democrats blame for luring votes from their candidate, Al Gore, in 2000, particularly in Florida. President Bush won the state and thus the election by a narrow margin.
Mr. Nader "obviously did that in 2000, so the role of these niche parties is greatly elevated," said Mr. Ciruli.
Mr. Barr was locked in a dead heat with Miss Ruwart after the fifth ballot, but then announced that he would support Mr. Root, who was the third-place candidate, as his running mate.
The move appeared to swing many of Mr. Root's delegates to the Barr camp, giving him the support he needed to overcome Miss Ruwart's challenge.
According to party rules, the vice-presidential candidate is chosen by the convention delegates. Five candidates, including Mr. Root, were in the running.
Earlier, Mr. Root made an impassioned plea for the vice presidency after losing on the fifth ballot, saying he wanted to spend the next few years "learning from the master" in a Barr administration.
Supporters began to chant, "Barr-Root," after Mr. Barr's nomination was announced.
Eliminated in a previous round was former Sen. Mike Gravel of Alaska, who ran for the Democratic presidential nomination this year before switching to the Libertarian Party in March.
After his defeat, Mr. Gravel, 78, announced his retirement from politics, a career that spanned more than 50 years and included two terms in the U.S. Senate. A longtime antiwar activist, Mr. Gravel might be best known for reading the Pentagon Papers into the Senate record in 1971.
"I started out in politics when I was 15, and this is the end of my political career," said Mr. Gravel, adding that he will continue to write and lecture on his pet causes.
• This article is based in part on wire service reports.