A sought-after Chicagoland district will host the state’s most competitive primary, as four GOP hopefuls are feuding to take on Rep. Bill Foster, a Democrat, in 2014.

Until recently, Republicans viewed state Rep. Darlene Senger as the GOP front-runner in the 11th District. But according to interviews with more than a half-dozen Illinois Republican operatives, local pols say her lackluster fundraising since she entered the race in April has impeded her ability to clear the field.

“This is the only real Republican congressional primary to watch in the state,” said Illinois Republican operative Ryan McLaughlin.

With Monday’s filing deadline passed and the primary just three months away, Senger faces a crowded field for the nomination. It now includes a deep-pocketed opponent who could seriously complicate her path to victory on March 18.

Earlier this year, Senger faced only local school board official Chris Balkema and radio host Ian Bayne. But Bayne and Balkema, who Republicans say is the tea-party-aligned candidate in the contest, also struggled to raise money for their bids.

A month ago, businessman Bert Miller entered the primary, and operatives say he is likely to be Senger’s largest obstacle to the nod.

“Darlene is very bright and tenacious as hell, some call her a bulldog in that mentality, and that’s … what [voters] want,” one local GOP operative said. “But if Bert Miller raises more money, things look bleak for someone like Darlene because Bert will be on TV and she won’t.”

Republicans describe Senger as a popular state legislator who has survived challenges in her state House district in the past. She has also received plaudits from the National Republican Congressional Committee, which recently placed her “On the Radar” of candidates — the first step of its tiered program to boost promising GOP candidates.

Miller owns a bottle cap manufacturing plant in the district and has close ties to the powerful Illinois Manufacturers’ Association. In a phone interview, Miller confirmed he’s raised more money in the few weeks since announcing his candidacy than the $160,000 Senger raised in the six months she’s been in the contest. The next fundraising reports are due Jan. 31.

“The largest train station on the metro line is across from [my factory]. As the train goes rolling by, they’ll see a big sign, Bert Miller for Congress. I’m not worried about getting the name out,” Miller said. “Darlene talks about how long she’s been running, maybe she should be worried how come she hasn’t got more inertia given how long she has been running.”

In a Wednesday phone interview, Senger said she’s getting help from GOP Reps. Ann Wagner of Missouri and Diane Black of Tennesee in her race. She cautioned that although the primary isn’t an ideal situation, she’s working hard to raise money and is confident she can get through to the general.

“I’ve been through some tough races, really tough races,” Senger said. “In ’08 with Obama on top of the ballot, that was also the year here that Speaker [Michael] Madigan wanted to get the supermajority in the [state] House and he needed four seats and mine was one of them. And so I totally get how these things work and what you’re up against. And boy, if you don’t know that going into this, you’re in for a rough ride.”

The 11th District includes exurbs southwest of Chicago, as well as two Democratic strongholds — Aurora and Joliet. Foster defeated Rep. Judy Biggert, R-Ill., by 18 points last year.

But Republicans are encouraged by their prospects there anyway. Democratic voters drop off significantly in the district in non-presidential cycles. Also, Senger and Miller boast the kind of moderate backgrounds that Republicans say are necessary to win there.

They also argue a fundraising edge is necessary in a general election against Foster.

Not only is Foster a self-made businessman with $591,000 in the bank, but the 11th District is an expensive area to run television spots. It includes the pricey Chicago media market.

“Senger’s people argue her narrative plays a really good contrast to Foster,” one local Republican operative said. “Obviously, she’s a woman who has been involved in politics for a long time. She was part of the conference committee on pension reform, so she can talk about that. However my feeling is you need to have someone who can raise money in a district that’s tough.”

To be sure, Miller — a political unknown — will still have a tough road to defeat Senger, whose name has been on the ballot before in a chunk of the district.

But if Miller wins the primary, it wouldn’t be the first time this cycle that a self-made businessman upset a House race — especially in Illinois. Foster accomplished a similar feat when he won a special election in 2008.