Senate Democratic leaders have been urging some of their Members to reject bipartisan entreaties from endangered Republican incumbents who are seeking legislative accomplishments to tout back home in this election year.

Sen. Gordon Smith (R-Ore.) said this week that Senate Finance Chairman Max Baucus (D-Mont.) rejected his offer to negotiate on a bill intended to prevent a pay cut for doctors who treat Medicare patients.

“I had offered to be the lead Republican and help them get votes. And I was told that I was not allowed to be,” said Smith, who faces a tough re-election race this year. Smith said Baucus cited his re-election status as the reason his request was refused.

Other vulnerable Republicans declined to be specific about whether they too have been shut out of bipartisan negotiations, but Smith said he wasn’t the only “targeted” GOP Senator who was getting the cold shoulder from Democrats.

“It’s the most petty kind of partisanship,” Smith charged.

Senate Majority Whip Dick Durbin (D-Ill.) said Democrats do not have a stated policy on not working with endangered Republicans, but he allowed, “In fairness, we understand what’s at stake here, and that’s the majority in the Senate.”

Senate Democratic aides said the informal policy is employed on a case-by-case basis, not universally.

The advice to Senators has been, “Don’t let yourself be used by Republicans,” explained one senior Senate Democratic aide. “All these [GOP] Senators get bipartisan religion when it’s an election year.”

Senate Democratic aides also cautioned that both parties have historically engaged in the practice. They acknowledged that it might seem more pronounced on the Democratic side this year because there are so few endangered Senate Democrats.

“This is a long-standing practice in the Senate,” one former Senate Democratic aide said. “When elections come around, you try not to give vulnerables anything to point to.”

The 2008 cycle is a difficult one for Republican Senators, with about 23 GOP-held seats in play and about a half-dozen incumbents in peril. Democratic Senatorial Campaign Committee Chairman Charles Schumer (N.Y.) has said Democrats are in a good position to pick up five to eight seats this year, many of them by beating incumbent Republicans.

Senate Democrats are clearly aware of the GOP’s difficulties, and Senate Majority Leader Harry Reid (D-Nev.) in particular has balanced his party’s interests against the need to rack up bipartisan deals.

Even so, bipartisanship has been rare during the 110th Congress. Senate Republicans appear resigned to filibustering nearly every Democratic initiative, while Democrats seem content to stop the GOP from offering amendments on most bills.

In Smith’s case, he ultimately signed on as an original co-sponsor of Baucus’ Medicare measure, which also seeks to increase Medicare benefits for low-income seniors. Sen. Olympia Snowe (Maine) — who is not up for re-election this year — served as the lead GOP sponsor. A majority of Republicans blocked the bill from coming to the Senate floor last week, arguing they supported a similar bill sponsored by Finance ranking member Chuck Grassley (R-Iowa).

Smith said it was clear to him that Baucus’ snub came from Senate Democratic leaders and not the chairman himself.

“I think he felt terribly about it,” Smith said. “I think he appreciates that this is about putting politics ahead of the needs of seniors.”

Baucus avoided a question about what he told Smith but did not dispute Smith’s account. “He’s done a great job on this bill. I admire his work,” Baucus said.

Sen. Norm Coleman (R-Minn.), who is facing a strong Democratic challenge this fall, said that while he’s “sensitive to the fact that it’s out there,” he continues to work with moderate Democrats to get bills passed. Citing Arkansas Sens. Mark Pryor and Blanche Lincoln and Indiana Sen. Evan Bayh as Democrats he’s worked with of late, Coleman said, “There are certainly folks I’ve worked with and will continue to work with” this Congress.

Sen. Susan Collins (R-Maine), whose reelection prospects remain strong despite a spirited challenge from Rep. Tom Allen (D), said she has not felt marginalized because she is on the ballot this year. Collins noted that she just introduced a bill with Sen. Hillary Rodham Clinton (D-N.Y.) and worked with Bayh and Sen. Ben Nelson (D-Neb.) on a measure to force the Iraqi government to pay more of the country’s reconstruction.

Several Senate Democrats said they hadn’t gotten the message that they should be shunning vulnerable Republicans.

“I haven’t heard it, but if I heard it, I’d ignore it,” Nelson said.

Even Durbin said he personally continues to co-sponsor bills “with Senators that want to work with me. Individual Senators may look at it differently.” Durbin added that he has recently co-sponsored bills with two GOP Senators up for re-election — Smith and Sen. Elizabeth Dole (N.C.).

But it appears that Durbin’s leadership position didn’t spare Smith from being airbrushed from an Iran sanctions bill that he and Durbin co-sponsored. The Finance panel marked up a nearly identical bill Wednesday only after reintroducing it as a chairman’s mark without Smith’s name attached. The ploy was intended to prevent Smith from taking credit for the measure, one Senate Democratic aide confirmed.

But Republicans aren’t the only ones being avoided this cycle. The Democrats’ only vulnerable incumbent, Sen. Mary Landrieu (La.), said she is definitely feeling the chill from Republicans when she attempts to work across the aisle.

Pointing to a tax relief measure for Louisiana and Mississippi homeowners who received grants in the wake of Hurricanes Katrina and Rita, Landrieu said she’s baffled that she can’t even get her home-state GOP colleague to team up with her. “I can’t get one Republican,” Landrieu said. “I’m begging the Republicans to come help us. I can’t even get [Louisiana Sen.] David Vitter. I continue trying to reach out to them.”