The more than 1,300 DFL activists who gather in Duluth this weekend to endorse a gubernatorial candidate will have to make one of the toughest choices their party has faced in years.

Two political heavyweights -- Minnesota House Speaker Margaret Anderson Kelliher and Minneapolis Mayor R.T. Rybak -- are expected to slug out an endorsing battle that could go late into Saturday night.

After 20 years out of power and nearly eight years under Republican Gov. Tim Pawlenty, delegates have a powerful thirst to endorse someone who, above all else, is electable.

Many delegates will be first-timers and an unusually high number are undeclared. Much may turn on who can most adroitly woo those last-minute deciders. Lining up behind Kelliher and Rybak are other substantial candidates whose followers could tip the balance if released to back a front-runner. It all promises to be an intrigue-laden weekend for politics watchers.

"More than any convention that I can remember in a while, it really is going to come down to what happens Friday and Saturday," said Rybak campaign manager Tina Smith, a convention veteran. "Usually more of the cards are dealt."

One of the biggest questions looming over Saturday's voting: What is the potential impact of the "Three Thirds" -- the trio of gubernatorial candidates who claim to be tied for third in the running delegate counts -- and their supporters.

State Sen. John Marty and state Reps. Paul Thissen and Tom Rukavina acknowledge that they walk in behind the two front runners. But they maintain that they have significant backing of their own. All have pledged to drop out of the race if they fail to win endorsement.

Convention rules will force any candidate who drops below a certain threshold of voting strength to withdraw, so expect a quick, initial cull of the field.

All three are hoping for a strong initial showing and then a scramble to pick up enough supporters to prevent an early departure. At the same time, Rybak and Kelliher will work to pick up the support that could put them over the top.

A new political coalition, reNEW Minnesota, has picked three favorites -- Thissen, Kelliher and Rybak -- but is holding its cards until after convention voting starts. The group hopes to move its bloc of potentially more than 100 votes behind a single candidate at a crucial point in the balloting.

Surfacing on the convention's edges will be two more candidates who are primary-bound: Former U.S. Sen. Mark Dayton, who says he'll pay his respects to delegates on Friday but won't put his name in contention, and former House Minority Leader Matt Entenza, who will be in Duluth explaining why he wants their endorsement, but who won't abide by their pick if it's not him.

No clear path

Despite the energy spent on convention politics, for the eventual endorsement winner, a DFL nod is only the beginning.

The endorsed candidate will have to survive a crowded August primary before he or she can face the general electorate in November.

Entenza, who can draw on his family fortune, has already upped the primary ante with a $100,000-plus television ad buy that will start next week. Dayton has similarly deep pockets, and Ramsey County Attorney Susan Gaertner also plans to enter the primary, where she could take a little shine off Kelliher's appeal to women if the House speaker wins endorsement.

Despite the cash advantage Entenza and Dayton may have, DFL party Chair Brian Melendez appeared confident that the convention's choice will win the August election.

A list of gubernatorial candidates going back to 1944, he said, shows that all but one was contested and that the DFL-endorsed candidate won all but three of the races.

"It's nice that other people want to run, but they are not going to win the primary," he said. "It's better if they realize that sooner rather than later."

Erik Peterson, a veteran activist who is running the floor operation for reNEW Minnesota, said he can't recall a time when someone not in the top two wound up with the endorsement prize. But he said that this year it may be possible.

Remarks like that are enough to keep the "three thirds" believing and all have the chops to be taken seriously.

• Marty, a seven-term veteran senator from Roseville who ran for governor in 1994 and lost miserably, has a solid and passionate activist following that believes in his universal health care, squeaky clean ethics and anti-corporate-subsidy stances. "My whole task at the convention is that they vote for what they believe," Marty said. Some of his fervent followers may settle for no one else.

• Rukavina, a 12-term House member from Virginia, with Iron Range roots and a style that keeps listeners awake and cheering, has dubbed his campaign "Refreshingly Honest." His humor -- he's selling American-made, union-printed Rukavina boxer shorts -- comes wrapped in a serious message of jobs, labor might and fight that appeals to many delegates. "Give me your vote and then stick with me," Rukavina told DFLers Wednesday.

• Thissen, a four-term House member from Minneapolis, is looking to become the consensus candidate who can draw from all. The Harvard-educated attorney has cut himself a health care speciality in the House and his calm, never-quit attitude may attract delegates. "We are picking up a bunch of delegates a day," he said last week.

Who would their supporters drift to if they get knocked out? Marty said that even if the candidates try to direct their supporters to someone else, it may not matter.

"Democrats are kind of an independent bunch," he said.

Rachel E. Stassen-Berger • 651-292-0164