ALEXANDRIA, Va./WASHINGTON (Reuters) - President Barack Obama made another push to sell his healthcare overhaul to a skeptical public on Tuesday, calling it a victory over special interests that will help the middle-class and defending the “courage” of legislators who backed it.

“This day affirms our ability to overcome the challenges of our politics and meet the challenges of our time,” Obama told a college audience outside Washington, as he signed into law the final changes to the sweeping plan approved by lawmakers last week, along with reforms in college student loan programs.

The signing capped a year-long struggle between Obama’s Democrats and the Republicans, who have vowed to repeal the healthcare bill, that has set the stage for a bitter campaign for control of Congress in November.

Democrats have a majority in Congress, but Republicans are hoping to make gains later this year and have vowed to make the healthcare bill the centerpiece of the election battle.

Obama defended lawmakers who voted for the bill, the most sweeping shift in U.S. social policy in decades, and took aim at what he said were misleading attacks.

“Courage is an essential ingredient in any landmark legislation, particularly when the attacks are as fierce and unrelenting and inaccurate as they have been over the past year. I just want to commend members of Congress who had the courage to do what’s right,” he said.

Opinion polls show Obama and his Democrats will have to work hard to promote the 10-year, $940 billion overhaul.

Nearly two-thirds of Americans say the plan costs too much and expands the government’s role too far into a private industry, according to a USA Today/Gallup survey published on Tuesday.

An insurance industry trade group said the law also does too little to address rising costs.

“The access expansions are a significant step forward, but this legislation will exacerbate the health care costs crisis facing many working families and small businesses,” Karen Ignagni, president of the America’s Health Insurance Plans group, said in a statement.

AHIP had also said on Monday that it would fully comply with regulations under the new law that banned excluding children from coverage if they had pre-existing health conditions. The New York Times had reported that insurers were arguing that at least for now they did not have to comply with that provision of the law.

In an interview that aired on Tuesday, Obama acknowledged that adjustments will be needed in the law to reduce costs.

“I think it is a critical first step in making a healthcare system that works for all Americans,” Obama said in an interview on NBC’s “Today” show. “It is not going to be the only thing. We are still going to have adjustments that have to be made to further reduce costs.

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U.S. companies have started to tally up the financial hit they say they will take because of the law.

The government still pays subsidies to large firms to help pay for prescription drug benefits for their retirees, but the new law does not allow the corporations to also deduct the amount of the subsidies from their taxable income.

Corporate America calls the change a tax increase, but the White House says it merely closes a tax loophole.

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John Boehner, who leads Republicans in the House of Representatives, said Obama signed “job-killing government takeovers.”

“Employers across the country are continuing to reveal the costly fallout from ‘ObamaCare’ - including new tax hikes and mandates that make it harder to hire new workers, and put health care benefits promised to workers and retirees in jeopardy,” he said in a statement.

Obama is to travel to Maine later this week for another event to tout the healthcare plan.