Unsure of the field and hesitant to endorse a loser, Congressional Republicans are remaining noticeably neutral in their party’s 2012 presidential primary.

Just six weeks before the first votes are cast in Iowa, only 66 GOP Members have publicly backed a candidate, compared with 111 at this point four years ago.

In interviews, Republican Members and GOP strategists credited low participation in the primary to Congress’ poor approval ratings, a general lack of enthusiasm for nominal national frontrunner Mitt Romney and minimal confidence that any of the former Massachusetts governor’s opponents can beat him.

“I want to wait and see who appeals to the grass-roots conservatives, and so far, that hasn’t happened. I’d like to be able to say I’m supporting conservatives around the country with this candidate,” said Sen. Jim DeMint, an influential Republican who announced earlier this month that he would not endorse in the primary. DeMint’s backing is coveted for both his national reach and his position representing South Carolina, a key early state.

DeMint, who endorsed Romney in 2008, is not alone among his Senate Republican colleagues from early primary and caucus battlegrounds. Sen. Chuck Grassley (Iowa) also decided not to endorse in the race, as did Sen. Marco Rubio (Fla.). Sen. Dean Heller (Nev.) said he doesn’t endorse as a matter of policy. Sen. Lindsey Graham (S.C.) and outspoken conservative Rep. Steve King (Iowa) are on the fence, and neither seems in a hurry to weigh in. Sen. Kelly Ayotte (N.H.) seemed hesitant to pick sides in an interview with Roll Call last week but then endorsed Romney over the weekend.

That Congress is held in low regard — with a job approval in single digits in some surveys — has made Republican presidential candidates less eager to seek and tout Member support. The feeling is mutual, with Members lukewarm on anchoring their political fortunes to a White House hopeful.

Romney is the only contender with a concerted whip operation, led by Sen. Roy Blunt (Mo.).

One GOP Member said that most Republicans on Capitol Hill expect Romney to be the nominee but that there “is not the same enthusiasm” for him as there has been for frontrunners in the past. Republican strategists with relationships in the House and Senate said Members have been equally indifferent about the rest of the field.

Whether they are concerned that Romney’s moderate image could generate friction with conservative activists back home or are worried that other candidates aren’t viable, Members have felt more comfortable standing pat.

“Members who backed [Texas Gov.] Rick Perry are now in a difficult position of defending him and no one wants to repeat that kind of mistake,” said one GOP operative who is not affiliated with a candidate.

Once considered a frontrunner, Perry has seen his star fade as he has continued to make embarrassing blunders during primary debates.

“I think we just need to let the whole primary process play out, so I’m not planning on endorsing anybody anytime soon,” explained Sen. Ron Johnson (Wis.), who was elected last year on the strength of tea party support. “There’s still a lot of information I need to see play out here. We still have debates, we’ll see how some of the voters respond; there’s no reason to jump to a conclusion right now.”

Recent national polls show former Speaker Newt Gingrich joining Romney in the lead, even though the Georgian’s campaign appeared on the verge of collapse in June following high-profile defections of his campaign staff.

Georgia businessman Herman Cain still polls near the top, but his trend is negative in the wake of sexual harassment charges and foreign policy gaffes. Rep. Ron Paul (Texas) is also surging in some of the latest surveys, including polls gauging support in the early-voting caucus and primary states.

The fluid race has seen Rep. Michele Bachmann (Minn.) poll well early in the summer only to drop off. Perry also tanked after entering the race in mid-August as the candidate to beat. The RealClearPolitics.com average of all national polls issued Nov. 8 to Nov. 15 showed Romney with 22 percent, Gingrich with 21.6 percent, Cain with 18.6 percent, Perry with 8.2 percent, Paul with 7.8 percent and Bachmann with 5.4 percent.

Sen. John Thune (S.D.), one of many high-profile Republicans to consider and then decide against running for president in 2012, said the failure of the contest to solidify, or for a consensus candidate to emerge, has added to Members’ uncertainty about whether to endorse.

“I want to have somebody who’s a principled conservative and who can articulate our vision effectively. But I also want to make sure that we’ve got somebody who can win in ’12,” said Thune, who was active for Sen. John McCain (R-Ariz.) in 2008.

House Republicans have been more willing than their Senate counterparts in the endorsement sweepstakes, but only slightly. Lawmakers who usually relish being intimately involved in a presidential campaign are staying mum. House Rules Chairman David Dreier was an influential backer of George W. Bush in 2000 and 2004, and he was an early, active supporter of former New York Mayor Rudy Giuliani in 2008.

But the California Republican is neutral in this contest. In a brief interview last week, Dreier said his previous involvement in presidential primaries occurred “back when the endorsement of a Member of the United States Congress was a positive.”

But announcements of support could begin to accelerate in December. McCain said he’s been taking more calls from fellow Members asking advice on getting involved in the primary, and Blunt said he’s begun to see movement in his bid to gather Capitol Hill support for Romney. But the Missourian noted that his whip operation has virtually no competition. Sen. John Hoeven (N.D.) endorsed Romney on Friday.

A Republican strategist with House and Senate clients said institutional support has increasingly gravitated toward Romney as donors and high-level operatives conclude that he is positioned to win the nomination. According to Roll Call’s endorsement list, Romney has received the backing of 42 Members; Perry has garnered 14, including eight Texans; Gingrich has 6, among them four Georgians; and Paul has three, including his son, Sen. Rand Paul (R-Ky.). Rep. Dan Benishek (Mich.) is Cain’s single supporter. Bachmann has no publicly announced backers.

“Everything has been a little slower this time,” Blunt said. “I think Members are legitimately figuring how much of their own political capital they can transfer, and that is a post-2010 phenomenon in my view.”