WASHINGTON — The White House has begun an aggressive campaign to use approaching Supreme Court arguments on the new health care law as a moment to build support for the measure seen as President Obama’s signature legislative achievement, hoping to shape public opinion on an issue at the center of the battle for the White House and Congress.

On Wednesday, White House officials summoned dozens of leaders of nonprofit organizations that strongly back the health law to help them coordinate plans for a prayer vigil, press conferences and other events outside the court when justices hear arguments for three days beginning March 26.

The advocates and officials mapped out a strategy to call attention to tangible benefits of the law, like increased insurance coverage for young adults. Sensitive to the idea that they were encouraging demonstrations, White House officials denied that they were trying to gin up support by encouraging rallies outside the Supreme Court, just a stone’s throw from Congress on Capitol Hill. They said a main purpose of this week’s meeting, in the Eisenhower Executive Office Building adjacent to the White House, was to give the various groups a chance to learn of the plans.

For months, Democrats in Congress and progressive groups have urged the White House to make a more forceful defense of the health care law, which is denounced almost daily by Republican lawmakers and presidential candidates.

Administration officials said that they would much prefer to focus on job creation and the need for clean energy at the moment and that the court arguments were forcing health care to the forefront. But they appear to have decided that they cannot risk allowing the court proceedings to unfold without making sure that backers of the sweeping overhaul will be prominent and outspoken.

Opponents of the law will be active as well and are planning to show their sentiments at a rally on the Capitol grounds on March 27, the second day of Supreme Court arguments. Republican lawmakers, including Senator Patrick J. Toomey of Pennsylvania and Representative Michele Bachmann of Minnesota, are expected to address the rally, being organized by Americans for Prosperity, with support from conservative and free-market groups like the Tea Party Express.

At the White House meeting on Wednesday, a wide range of advocates representing consumers and people with diseases and disabilities — as well as doctors and nurses, labor unions and religious organizations — discussed plans to bolster the landmark law, which is being challenged by 26 states as unconstitutional.

Supporters of the law plan to hold events outside the court on each day of oral argument. The events include speeches by people with medical problems who have benefited or could benefit from the law. In addition, supporters will arrange for radio hosts to interview health care advocates at a “radio row,” at the United Methodist Building on Capitol Hill.

People who attended the meeting on Wednesday said the speakers included Jennifer Palmieri, deputy communications director at the White House; Jon Carson, director of the president’s Office of Public Engagement; Jeanne M. Lambrew, deputy assistant to the president for health policy; and Mark B. Childress, a deputy chief of staff at the White House.

“The White House was very encouraging and supportive of our activities,” said Ronald F. Pollack, executive director of Families USA, one of more than 60 organizations that sent representatives to the meeting.

Mr. Pollack said the theme of events at the Supreme Court would be, “Protect our health care, protect the law.”

Jennifer M. Ng’andu, a health policy specialist at the National Council of La Raza, a Hispanic rights group, said White House officials emphasized that the court case provided “a great opportunity to highlight benefits of the law for real people.”

A White House official who attended the session said that at least 100 people were present, but he declined to provide a list of their organizations.

Nicholas Papas, a White House spokesman, confirmed that “outside organizations came together to share with the White House and each other the activities they have planned.” In coming weeks, he said, “the administration will continue to implement the law and educate the public about the benefits of health reform.”

In the week before the Supreme Court arguments, administration officials will fan out around the country and join local groups in celebrating the second anniversary of the law, signed by Mr. Obama on March 23, 2010.

Just after the law was signed, Senator Charles E. Schumer, Democrat of New York, predicted on the NBC program “Meet the Press” that “those who voted for health care will find it an asset, those who voted against it will find it a liability.”

But two years later, public opinion on the law is deeply divided, and polls show significant opposition among Republicans and independent voters in battleground states.

Backers of the law said they would use data supplied by the White House to show how the law had reduced drug costs for older Americans, guaranteed free preventive care for millions of people and allowed many children to stay on their parents’ insurance policies.

However, one of the main provisions on which the Supreme Court will focus — a requirement for most Americans to carry health insurance — is not particularly popular, according to opinion polls.

The court is expected to issue its decision in late June, as the presidential campaign enters its crucial final months and Congressional races grow more intense.

Groups working with the White House include the Service Employees International Union; the American Federation of State, County and Municipal Employees;  Health Care for America Now, a consumer coalition that fought for passage of the legislation; Protect Your Care, a nonprofit group created last year to defend the 2010 law; and the Center for American Progress, a research and advocacy group with close ties to the White House.

Eddie P. Vale, a spokesman for Protect  Your Care, said White House officials at the meeting “sounded pretty excited about the size and scope” of efforts to promote the law this month.

Levi Russell, a spokesman for Americans for Prosperity, said buses would bring people to rally against the health law from Maryland, Michigan, New Jersey, New York, North Carolina, Pennsylvania and Virginia, among other states. The theme is “Hands off my health care.”

On its Web site, the Obama re-election campaign describes Americans for Prosperity as a “special-interest front group run by the oil billionaire Koch brothers.” In a recent fund-raising appeal, Jim Messina, the campaign manager, said that the oilmen, Charles and David Koch, were “obsessed with making Barack Obama a one-term president.”

Mr. Russell said, “The Koch brothers were involved in the founding of Americans for Prosperity and contribute to it, but they are just two out of 90,000 donors.”