While conservatives on Capitol Hill are waging a last-ditch battle to scuttle the Affordable Care Act, some powerful Washington groups that were among the legislation’s loudest critics are now trying to shape the law and how it’s carried out, an acknowledgment that they need to learn to live with the landmark initiative.

Other players that have been more supportive of the law are also engaged in a lobbying push, pressing Congress and federal agencies to refine provisions.

“Why shoot for the moon?” said Randel Johnson, senior vice president of the U.S. Chamber of Commerce, a vocal critic of the law and Washington’s biggest spender on lobbying. “There may be five or six things we can get done — those are the ones we’re going to focus on.”

Several elements of the law the Chamber still wants to change are significant, such as repealing the employer mandate and cutting new taxes it imposed. But the group’s current stance marks a break with the Chamber’s all-out opposition to the law when it was being debated in Congress and reviewed by the Supreme Court.

For the Chamber and other employer groups, a top priority is revising the law’s definition of full-time workers, from those who work 30 hours per week to 40 hours. Under the law, large employers are required to provide health insurance to full-time workers.

For hospitals, the focus is delaying cuts to payments they receive from the government for caring for low-income and uninsured patients, given that fewer of them may start getting insurance coverage as the result of the law than previously projected.

And an array of business interests wants to repeal the 2.3 percent excise tax on medical devices that was enacted to help pay for the health-care initiative, arguing that the tax will cost jobs and stifle innovation. A House measure that would do that has 260 co-sponsors but has not yet been taken up by the Ways and Means Committee. A similar proposal has been backed by the Senate in a nonbinding resolution.

Still drafting regulations

Big pieces of legislation typically require what one top lobbyist called “refinements or improvements or corrections,” and, with the health-care program, a main target of lobbying is the Centers for Medicare and Medicaid Services, which is still drafting regulations to carry out the law. While few involved expect quick progress, they are all keenly aware of the approach of Oct. 1, when people are supposed to be able to start signing up for health plans through online marketplaces.

“Most of the health-care industry is trying to figure out from a commercial standpoint how to work with the law, because they have to,” said Dan Mendelson, a former Clinton administration health official who is chief executive of Avalere Health, which advises companies on how they could be affected by proposed regulations.

The health-care industry has long been among Washington’s top-spending sectors when it comes to lobbying, and three years after passage of the law, that remains the case. In the first six months of this year, the industry spent $243 million on lobbying, according to disclosure records compiled by the Center for Responsive Politics.

Former Obama administration officials and others who helped formulate the law are in heavy demand. Among them is Yvette Fontenot, who wrote key elements of the Affordable Care Act while a Senate staffer and then worked on the law at the White House and the Department of Health and Human Services. Her lobbying clients include the Blue Cross and Blue Shield Association and Express Scripts, which manages prescription benefits.

Elizabeth Fowler helped develop the Senate version of the health-care plan and then worked at the White House on implementing ­changes to the insurance market. While not a registered lobbyist, she works for Johnson & Johnson, guiding the company’s global health policy.

‘Always another round’

“Regulations can be shaped by directly engaging with the agency, or with the White House or Congress as a bank shot to influence the agency’s decision-making,” Mendelson said. And while little is moving in Congress these days, advocacy doesn’t stop. “There’s always another round to be fought if at some point things do open up,” he said.

Such efforts to shape the bill have already had some success. When the administration made the surprise announcement in July that it would delay enforcement for one year of a key requirement that large employers provide coverage to their workers, White House officials said they were listening to businesses that said they needed more time to comply.

But it’s particularly difficult to get things done on Capitol Hill when it comes to the health-care bill.

“Democrats are loath to open up the Affordable Care Act, and Republicans are loath to want to perfect it,” said Rick Pollack, executive vice president of the American Hospital Association, which spent more than $17 million on lobbying last year, according to federal disclosure reports.

Nonetheless, Pollack’s group has a “fix-it” list that it hopes to see acted upon, including getting the government to hold off on reducing payments to hospitals that serve large numbers of low-income and uninsured people. The hospital association argues that because the Supreme Court ruled last year that states can opt out of a planned Medicaid expansion and other factors, there will be more rather than fewer low-income and uninsured people going to hospitals.

Last week, as part of the International Franchise Association’s annual public affairs “fly-in,” about 325 members — including Dunkin’ Donuts, Lawn Doctor and Jiffy Lube owner-operators — met with members of Congress and their staffs to urge them to support legislation that would redefine full time as 40 hours per week.

The franchise group opposed the health-care law, but a spokesman said it has changed its approach.

“We’re dealing in a political reality where the law is not going to be repealed until the political dynamic changes,” said Matthew Haller, a group spokesman.

Scott DeFife, the National Restaurant Association’s executive vice president for policy and government affairs, said there’s growing recognition among those involved of the massive effort required. “People understand that some of these very detailed elements in the law may not jibe,” he said.

The group has also been working with the Treasury and Labor departments to make sure regulations take into account seasonal fluctuations in restaurant employment when determining whether these enterprises are large enough to be required to insure their workers. And while the current guidelines provide some flexibility to restaurant owners, the association would like to see that written into law.

“The implementation of the Affordable Care Act is a three- to seven-year process,” DeFife said. “We’ve been working at this for a couple of years, and we’re going to continue working on it.”