WASHINGTON — In early spring, when the prospect of a global warming bill passing Congress seemed like an Al Gore pipe dream, President Obama invited Rep. Henry Waxman, D-Calif., to the Oval Office.

“He realized that this was a very tough bill to get through,” Waxman remembers.

At a time when some still saw Obama as too inexperienced to adapt to Washington’s back-room ways, Waxman found the new president perfectly ready to accept the only strategy that offered hope of success: Sitting down with each group affected by the bill and trading concessions for support.

That strategy yielded a narrow victory in the House. The question was, did Obama, Waxman and other supporters give away so much that the benefits to the environment ended up being slim to none — especially since the bill now goes to the even less sympathetic Senate?

“There’s a point at which you’ve got to ask yourself, what are we doing here? What’s the point?” said Elaine Kamarck, a former Clinton administration official and adviser to then-Vice President Gore, who now teaches at Harvard’s Kennedy School of Government.

So far, most major environmental groups are sticking with Obama. Most groups made the calculation that, in sum, the bill was worth moving, said Emily Figdor, the federal global warming policy director for Environment America.

“We think there’s a lot of problems in the bill,” she said, but “we need to take that first step. We’re so long overdue.”

If the bill makes it to the president’s desk, says its co-author, Rep. Edward Markey, D-Mass., “We will have fundamentally changed our relationship with energy and how it’s generated in this country.”

Even before Obama was inaugurated, Markey and Waxman had begun meeting with industry executives and others. They talked to farm groups. They talked to oil and natural gas executives, coal producers, manufacturers and others who could face higher energy costs— passed on to consumers in higher prices.

The goal of the bill they were drafting, embraced by Obama during the 2008 presidential campaign, was to establish government regulations that would ratchet down U. S. greenhouse gas emissions through a system of tradable emissions permits known as cap and trade.

It would set strict energy efficiency standards and a national requirement for renewable electricity use.

Against that background, Waxman, Markey and Obama’s representatives found that one thing made interest groups receptive: The Democrats were willing to deal.

That approach is fast becoming an Obama hallmark, a blueprint for the administration’s battles to come over health care, financial regulation and the climate fight in the Senate: A devotion to compromise, combined with finding a way to maintain strict discipline among hopeful but anxious liberals.

To attract House Agriculture Committee Chairman Collin Peterson of Minnesota and other Farm Belt representatives, Waxman and Markey agreed to sweeteners for farmers and other biofuel producers.

Then there was coal.

Waxman is an urban liberal, but his Energy and Commerce Committee is stacked with Democrats from districts that produce or consume massive quantities of the No. 1 contributor to global warming. Without those Democratic votes, no climate bill could even clear the committee.

The critical question concerned the permits that would allow companies to exceed emissions limits. Hundreds of billions of dollars were at stake. Coal and manufacturing groups wanted them handed out free, at least in the early years.

By the time the committee voted, shortly before Memorial Day, Waxman and Markey had agreed to give free permits to coal-hungry utilities, to oil refineries, to automakers and to manufacturers struggling to compete with China and India.

“That was an essential compromise,” Waxman said. “It would be very disruptive to the economy had we not recognized that certain regions of the country were heavily dependent on coal.”

Not everyone yielded to the Democrats’ blandishments. Several industry groups opposed them, including the U. S. Chamber of Commerce and the American Petroleum Institute.

But a host of companies and utilities touted the bill, including Nike, Starbucks, Exelon, Symantec and PG&E, a coalition that House Democrats said was invaluable.

“Many of the folks who are supporting the bill now from the private sector, that I know, said they didn’t think they’d be here today,” said Rep. Melissa Bean of Illinois, a pro-business Democrat who voted for the bill. “And they’re surprised at . . . how their concerns were listened to.”

Environmentalists watched the deals go down with varying cases of nerves. Greenpeace labeled the final bill “a victory for coal industry lobbyists, oil industry lobbyists, agriculture industry lobbyists, steel and cement industry lobbyists.”

An Environmental Protection Agency analysis this month suggested the bill would barely dent the nation’s oil imports. A study by the environmentalist Union of Concerned Scientists predicted the renewable electricity standard, watered down by compromise, might spur less wind and solar use than no standard at all.

Still, some of the largest conservation groups said the bill was a testament to their faith in Obama, Waxman, Markey and House Speaker Nancy Pelosi of California.