WASHINGTON » With political momentum behind an immigration overhaul flagging, advocates are counting on business groups to turn up the pressure on skeptical House Republicans who are much less susceptible to that lobby than they have been in the past.

The changed dynamic illustrates the difficulty of guiding immigration legislation through the House as well as the challenge for business interests to reassert themselves to the more ideological brand of congressional Republican.

"I’ve heard from all sides on the immigration bill, certainly our Kansas Chamber of Commerce," said Rep. Lynn Jenkins of Kansas, a member of the House Republican leadership. "But I will tell you, a majority of Kansans that I visit with are not as eager. And the power lies with the people, at least in Kansas."

The prickly relationship between House Republicans and business groups large and small will complicate efforts to move legislation to increase immigration of highly skilled workers, expand guest worker programs and establish a path to legalization or citizenship for the 11 million immigrants already in the country illegally.

Yet advocates of such a comprehensive approach say the business world may still be their last, best shot, and business groups are mobilizing for an immigration offensive expected to kick into high gear by August.

"The business community is solidly behind this — small business, large business, the chamber, the Business Roundtable, you name it, they’re all solidly in," said Sen. John McCain, R-Ariz., an author of the bill approved by the Senate last month. "We need them to weigh in, very frankly, on this issue, because we advertise ourselves as the party of business. Perhaps they can have some effect."

In a meeting Tuesday with seven of the eight senators who drafted the original bill and members of various advocacy groups, a frustrated McCain took business to the woodshed. Their efforts so far to lobby House Republicans, he explained in a stern tone, have not been sufficient. Their side is losing the battle to define the message, he said, and the next few months, including the August recess, will make or break the immigration effort.

This week, Speaker John A. Boehner said he welcomed any sales pitches from business, noting that the majority of House Republicans had never been faced with immigration legislation. "The more education that we have for our members, the better we’re going to be able to facilitate dealing with a very thorny issue," he said.

In a broad immigration overhaul, businesses desire an injection of highly skilled workers who have found it increasingly difficult to enter the country, an expanded pool of lower skilled but energetic immigrants and a way to legally employ workers in the country illegally who have been mainstays of the labor force in many parts of the country.

Many business groups have been working on the issue for more than a year. Last month, during the annual summit meeting of the National Association of Manufacturers, the group’s members held meetings with lawmakers to discuss immigration and other issues. Several of the association’s members, including Caterpillar and Cargill, recently participated in an immigration briefing for House staff members hosted by Rep. Robert W. Goodlatte, R-Va., the chairman of the House Judiciary Committee.

"It does us no good to bring in the best and brightest in the world, train and educate them, and then send them home," said Joe Trauger, the association’s vice president of human resources policy, in summing up the group’s message.

Last month, Goodlatte also met with 20 chief executives of some of the largest corporations in the country through the Business Roundtable, an association of major-company CEO’s, said Greg Brown, 52, the chairman and chief executive of Motorola, who heads the group’s immigration task force.

The Business Roundtable has strongly supported the Senate’s comprehensive approach, he said, and the chief executives "remain cautiously optimistic that as the House continues to progress and pass a series of independent bills, then after August there will be a mechanism to unify them with the Senate."

At the same time, the House’s approach has risks. High technology businesses strongly back an expansion of visas for skilled workers. Agribusiness and service industries are most interested in guest worker programs. In a comprehensive bill, like the Senate’s, all the business groups have an incentive to back the whole measure to make sure that their particular component remains. If the House separates the components, businesses could get behind some — but not all — of the piecemeal bills.

"You’ve got to keep a holistic momentum going because if you disaggregate, you run the risk of fragmentation," Brown said.

The most involved group has been the U.S. Chamber of Commerce, which helped broker a deal with organized labor on a guest worker program that was critical to the success of the Senate bill and ran national radio and television advertisements in the week leading up to the legislation’s final passage in the Senate. The group recently met with the 120 largest trade associations among its members to plot strategy. Engagement with local and state chambers of commerce has been constant.

"The goal is to get a duplicate message, an echo chamber," said Bruce Josten, the chamber’s longtime chief lobbyist.

But, he said, "The House is entirely different from the Senate."

Business lobbyists say that hostility in the House may be overstated. Maybe 40 to 60 conservative legislators view business groups based in Washington with suspicion, but many of them were never going to side with business on immigration.

Still, the skepticism toward business is pervasive in certain sectors. Some Republicans, especially those who came into the House in the Tea Party wave of 2010, are instead looking to conservative groups like Club for Growth and Heritage Action for guidance.

"So many of them have come to the well so many times for their corporate welfare handouts that they have lost all credibility with the base of the Republican Party," said Rep. Mick Mulvaney, R-S.C. "The days of the Chamber of Commerce being the gold standard may be coming to an end if they aren’t already in the past."

Indeed, when they have had the chance, Republicans have relished the opportunity to strike a populist stance against big business. The entire House Republican leadership has been castigating President Barack Obama’s decision to delay for a year the mandate that large employers buy their workers health insurance, but press on with an insurance-buying mandate for individuals.

"Obama gave big business a pass," Jenkins said in an interview. "That was a major shift. The administration represents big business."

Club for Growth does not see itself as a business group, said its president, Chris Chocola. "We’re a pro free-market group," he said, which is not always in line with business interests.

Club for Growth does do one thing that explicitly pro-business groups do not. "We participate in primary elections; they don’t," Chocola said. "And the greatest motivating factor for a member of Congress is keeping their job."

To that end, many business groups are trying to reach members of Congress where it matters most — in their home districts. John Feinblatt, the chief policy adviser for Mayor Michael R. Bloomberg of New York and chairman of the Partnership for a New American Economy, said his group has drawn up a list of roughly 40 House Republicans to watch, and the group plans to mobilize in 14 states, and even more districts, during the August recess.

"The bottom line is, this is not a fight that’s going to be won in Washington," Feinblatt said. "It’s going to be won in districts across the country as representatives hear from local business owners, from local chambers of commerce, from job creators at home, all saying that passing immigration legislation is crucial to the success of their local economy."