The rivals for an open seat in the U.S. Senate couldn't be more vintage Colorado: Democrat Ken Salazar (search) comes from a fifth-generation ranching family in the San Luis Valley; Republican Pete Coors (search) is an executive in a family brewing business synonymous with the Rockies' snowcapped peaks.

The similarities end there.

One of the most closely watched political races in the state's history has turned into a dogfight between two men who insist they could not be more different — on the war in Iraq, taxes, abortion, the death penalty. They even squabbled on national television about who started mudslinging first.

Behind all of it is a nationally funded campaign infused with negative TV ads to fill an open seat held by retiring Republican Sen. Ben Nighthorse Campbell (search).

Republicans hold a Senate majority of 51 to 48 and one independent. Colorado is among eight toss-up states that will determine whether they maintain, expand or lose that majority.

The election already is the most expensive in state history: Salazar has raised $6 million, Coors almost as much, including more than $1 million of his own fortune.

"We all predicted this would be very intense. If it's possible, it's even more intense than we originally thought," said Bob Loevy, a political science professor at Colorado College in Colorado Springs.

Salazar, a moderate who has won two statewide elections for attorney general, has maintained a slight lead in the polls, but the most recent was before Coors put another $500,000 of his money into the campaign last Friday.

A political neophyte, Coors, 58, entered the race in April at the urging of GOP leaders, who viewed former Rep. Bob Schaffer as too conservative to win a statewide race. He won a bruising primary campaign while Salazar, 49, cruised by his challenger, educator Mike Miles.

The 6-foot-5, silver-haired Coors is on leave as chief executive of the Coors Brewing Co., started by his great-grandfather and now the nation's third largest beer company. Well before the election, his face was on national TV ads that usually feature the Rockies or mountain streams gurgling in the background.

Some of his positions are not in step with the mainstream GOP. He opposes the death penalty, unlike Salazar, and raised eyebrows recently by suggesting Congress might have balked at authorizing war in Iraq "given what we know today."

President Bush brushed off the comment as he stumped for Coors the next day, saying he would be able to count on the beer executive "on the big issues."

As a candidate, Coors opposes gay marriage and adoption by gays. Coors the company is proud of its benefits for same-sex partners of employees and leading brand Coors Light can be found in ads targeting the gay community.

Salazar has styled himself as a pickup-driving champion of the people, wearing bolo ties, cowboy hats and boots on the campaign trail. His ancestors helped settle Santa Fe, N.M., four centuries ago and then moved to southern Colorado. He is one of two Hispanic candidates — the other is Republican Mel Martinez in Florida — who could end a quarter-century absence of Latinos in the Senate.

John Kerry had hoped a heavy Hispanic turnout for Salazar and his brother, John, who is running for a House seat, would benefit Kerry's presidential prospects in the GOP-leaning state. After appearing with Salazar last week in Pueblo, however, Kerry pulled his Colorado TV ads and canceled a second visit to the state.

Salazar's stances are remarkably similar to those of Kerry on everything from the war to ending tax incentives for companies that move jobs overseas. He has criticized the way Congress and the administration responded to threats before and after the Sept. 11, 2001, attacks.

Both Coors and Salazar are Roman Catholics, which flared briefly as an issue this year when church leaders criticized Catholic politicians who don't follow church doctrine. Coors opposes abortion; Salazar supports abortion rights.

Salazar's record as the state's natural resources chief and attorney general have been assailed, while Coors Brewing's downsizing and environmental violations have provided fodder for attack ads. No one issue has stuck.

The candidates split predictably on economic lines, with Coors saying tax cuts pushed by Bush should be made permanent while Salazar wants them rolled back for the very wealthy. Attacked in ads as a pawn of the trial lawyers, Salazar said he favors capping medical malpractice awards.