The conventional wisdom was that Peter Coors (search), the wealthy beer baron with a face for TV, would coast to the Republican nomination for Colorado's open Senate seat. And that Attorney General Ken Salazar (search), a veteran campaigner touting himself as a folksy farmer with deep Colorado roots, would grab the Democratic nod without a fight.

It hasn't been that simple: Attacked by conservatives in his own party, Coors is in a dogfight with former Rep. Bob Schaffer (search) for the nomination. Salazar has been in a rough fight with educator Mike Miles (search), a former Army Ranger who has been building grass-roots support across Colorado for two years.

Pundits have stopped trying to predict what will happen in Tuesday's primaries.

"I haven't a clue," said Floyd Ciruli, an independent political analyst who said both races are too close to call. He said Miles and Schaffer have an advantage among party activists, but Coors and Salazar are better known.

The race is being closely watched by national parties because the winner this fall could help determine which party controls the Senate. Republicans now hold a 51-48 majority, with one Democrat-aligned independent. Democrats view Colorado as one of the best opportunities to pick up a Senate seat.

Political experts say the fight for the seat being left open by the retirement of GOP Sen. Ben Nighthorse Campbell will be among the most expensive in Colorado history -- some $6 million for each side by Nov. 2.

A Denver Post poll published Friday showed Coors was favored by 45 percent of 400 likely GOP voters while Schaffer was backed by 41 percent. The lead falls within the poll's margin of error of 5 percentage points. Salazar, meanwhile, was favored by 67 percent Democrats to just 21 percent for Miles.

Miles surprised Salazar by winning top billing on the primary ballot at the state Democratic Party convention in June. The Democratic Senatorial Campaign Committee turned around and surprised Miles by refusing to back him -- or even acknowledge he was in the race.

On the issues, the two Democrats differ over Iraq, with Miles calling the war a mistake and Salazar backing the Bush administration's decision. They also fought over health care. Miles said the country needs a national health plan, something Salazar says would be a bureaucratic nightmare.

Salazar's campaign manager, Jim Carpenter, said Salazar has worked hard since the convention, courting activists and making sure his supporters get to the polls. Miles said he has campaigned for months and he expects his backers to deliver the nomination.

He faces daunting opposition: Salazar has raised the most money in the race, $2.9 million, compared to $321,367 for Miles. Salazar also has the support of the Democratic Senatorial Campaign Committee, which is hoping he can attract urban Hispanics to the polls in what could be a boon for presidential candidate John Kerry.

On the Republican side, Gov. Bill Owens surprised everyone when he rejected entreaties from party leaders to run. A succession of other prominent Republicans all demurred.

The governor turned to the deep-pocketed Coors, well known in the state and beyond for his appearances in bucolic beer ads. Coors, a married father of six, has touted himself as a family values candidate, surprising critics of Coors beer ads that include, among other features, sexy twin sisters.

Schaffer, who warned Coors not to challenge him for the "heart and soul" of the GOP, easily won top billing on the primary ballot, only to watch agape as Owens and other Republican leaders brushed him off as unelectable because of his strong conservative views.

The attack ads started soon after: Schaffer supporters criticized Coors' political inexperience and ridiculed his support for lowering the drinking age from 21 to 18 (he contends it would teach responsibility at a younger age). They also noted his support for same-sex couple benefits while heading his family's Golden-based brewery.

Coors fought back, accusing Schaffer of being a political insider and of padding his resume by claiming to be the director of a nonexistent bank. Schaffer's campaign said he is a paid director of a company that is organizing a bank. The two also differ on taxes and education.

"If you believe and think you're losing, you have no choice but to attack. More than half the time, that backfires on you," said Pat Fiske, Schaffer's campaign manager.

Coors said Schaffer is responsible for setting the acrimonious tone.

"I think it's unfortunate that what they're doing is legal, even though it's misleading and totally dishonest. If that's the kind of candidate people want, they'll win the election," Coors said.

Coors has a big financial advantage, raising $2.2 million to $769,000 for Schaffer and allowing him to splash his face on television ads across the state.

In another Colorado primary Tuesday, five Republicans are battling to succeed six-term GOP Rep. Scott McInnis. The Democrat in the primary is uncontested.