Two traditional sources of political power will be facing off when Arkansas voters head to the polls Tuesday to select a Democratic Senate nominee.

The power of incumbency will go head-to-head against the power of big labor in a grudge match that got very nasty very quickly in the race between Sen. Blanche Lincoln and Lt. Gov. Bill Halter. Arkansas Republicans are also going through a highly competitive primary, and the general election, regardless of who wins Tuesday, is expected to be very close.

Incumbency is limping into the Democratic primary fight after three-term Sen. Bob Bennett was given his walking papers at Utah’s Republican nominating convention last weekend and 14-term Rep. Alan Mollohan saw his long Congressional career come crashing down in the West Virginia Democratic primary this week.

But the race will also be a key test of the power of big labor, which has gone out on a limb to support Halter.

A strong showing by the lieutenant governor will be especially important for the Service Employees International Union and others who have spent millions backing his bid because another labor champion, Pennsylvania Sen. Arlen Specter, is in the fight of his political life that same night in a Democratic primary where the incumbent and labor find themselves on the same team.

In the Arkansas contest, Halter is clearly playing for a runoff, and recent polling shows it’s going to be close.

A candidate wins nomination outright in Arkansas if he takes more than 50 percent of the vote on primary night. If that doesn’t happen, the top two finishers head to a June 8 runoff.

The latest public polling from the Arkansas News Bureau showed Lincoln with 44 percent, Halter with 32 percent and 17 percent undecided. A little-known candidate is also competing for the nomination.

Halter spokeswoman Laura Chapin said Wednesday that she’s encouraged by those numbers because she believes the undecided voters will fall heavily in the lieutenant governor’s column.

“If [voters] haven’t decided in favor of a two-term Senator incumbent at this point, I would think they are ready for change,” she said.

She said Halter has been “steadily gaining momentum” and is “ahead of schedule” when it comes to where he wanted to be heading into Friday’s debate and the final weekend of campaigning.

But other data seem to paint a more static picture of the contest despite all the noise on radio and television.

A Daily Kos poll taken three weeks after Halter entered the race in early March showed Lincoln with 44 percent, Halter with 31 percent and 25 percent undecided.

“In his campaign it’s a victory all of a sudden that he moved a point,” said Arkansas Democratic consultant Robert McLarty, who is supporting Lincoln in the primary.

McLarty doesn’t expect to see any major swings in the final days.

“Everything including the kitchen sink has been thrown at both candidates. I don’t know what else you’re going to say that’s going to move anybody,” he said.

One difference between the Daily Kos poll and the Arkansas News Bureau survey is that farm loan broker D.C. Morrison was included in the latest poll. Morrision, who is running a mostly self-funded effort out of his own home, took 7 percent in the latest poll.

Several operatives questioned whether those who say they support Morrison — who has been equally critical of Lincoln and Halter in his campaign — will be motivated enough to get out and vote on Tuesday for a man who appears to be statistically out of the race.

If those voters do turn out, the effect will likely help Halter simply by taking some percentage of the overall vote off the table and making it harder for Lincoln to hit the 50 percent mark.

But if Halter does make the runoff, don’t expect Morrison to throw his support behind the lieutenant governor.

“If I don’t get it done then I will do everything I can to help the Republican win in the fall,” Morrison said Wednesday.

As Democratic insiders look to next week, one early indication of whether Halter will keep Lincoln under 50 percent may come from his performance in the counties outside his home base in Little Rock.

Because his greatest name ID is in Little Rock, Halter has spent much of his time introducing himself in Democratic strongholds like the Delta region and the counties in the far southwest part of the state. Halter spent Wednesday in Jonesboro, and Chapin said he would be spending very little time in Little Rock during the final week of the campaign.

If early returns show Halter competitive in the areas outside the Little Rock media market, it would probably be a sign that a runoff is in the works.

A runoff seems less likely for the Republican Senate nomination.

Polling indicates that Rep. John Boozman, who entered the contest in February, only needs a small percentage of the about 15 percent of undecided GOP primary voters to win the nomination outright Tuesday.

If the Republican contest does go to a runoff, it’s unclear whether Boozman would face state Sen. Gilbert Baker or former state Sen. Jim Holt, who was the GOP nominee against Lincoln in 2004.

Boozman would likely benefit in a runoff from the fact that the 1st district Republican primary appears to be the only GOP House primary in Arkansas headed for a runoff. That fact should help pull out more of his base if the contest goes until June.

Baker consultant Clint Reed said Wednesday that his camp is confident that after Baker gets to the runoff he can offer voters a clear choice between incumbency and change.

“Once it’s one candidate versus another candidate, the lights will shine on the difference between a Washington D.C., establishment candidate that has been part of the problem in Washington versus a guy who has balanced budgets and who is really a fresh face in the Republican party,” Reed said.

National Republican Senatorial Committee spokesman Brian Walsh, who expects Lincoln to emerge from her primary, said that regardless of the outcome of the GOP contest, Arkansas remains one of the top pickup opportunities for Republicans in November.

“The primary has forced Blanche Lincoln to give up the one remaining advantage she had in this race, which was her war chest,” Walsh said. “The financial playing field will be leveled, and she’s got to account for a record that is clearly very unpopular among her constituents.”

Democratic Senatorial Campaign Committee spokeswoman Deirdre Murphy responded that “all of the Republican Senate candidates in Arkansas are focused on one thing: blocking progress and siding with the corporate special interests.”