With the White House remaining tight-lipped on its invite list for today’s health care summit, business groups continued to scratch their heads Wednesday, wondering whether their invitations perhaps got lost in the mail.

“I’d actually like to know who’s going, but I’m completely in the dark,— said Larry Gage, chief executive officer of the National Association of Public Hospitals and Health Systems. Gage will be attending.

Exactly one week after releasing an ambitious $3.6 trillion budget blueprint, President Barack Obama this afternoon will convene the “White House Forum on Health Care Reform.—

This week’s hottest ticket downtown, the program’s secretive guest list has some health care executives nervous that their voices will not be heard when policymakers attempt to make good on an Obama campaign promise to provide “affordable, comprehensive and portable health coverage for every American.—

At Wednesday’s daily press briefing, Obama spokesman Robert Gibbs said the White House is expecting to host 120 participants at today’s summit but he did not provide specifics. The administration press office said a list of the conference’s participants would not be available until this morning.

“The president will open the forum, and participants will break out into several groups to discuss ideas on ways to reform the system, bring down costs and expand coverage,— Gibbs said. “The president will then reassemble participants in a closing session.—

But which groups will be among the 120 participants is less than clear.

As of press time Wednesday, the insurance industry’s primary lobbying outfit, America’s Health Insurance Plans, confirmed that it was attending the event, although it was uncertain whether individual providers would have a seat at the table.

An AHIP spokesman said Chief Executive Officer Karen Ignagni was attending, with plans to discuss Medicare, a federal health care program for seniors that is lucrative for many insurance companies.

“We recommend that the entire Medicare program, including [Medicare] Advantage needs to be evaluated,— spokesman Robert Zirkelbach said. “It’s going to require that all stakeholders come to the table. All stakeholders should be accountable for results, and we are committed to this process.—

The American Medical Association, which represents 250,000 physicians and medical students, also confirmed President Nancy Nielsen will attend, as will National Association of Children’s Hospitals President Lawrence McAndrews.

“The AMA is pleased to participate in the White House summit on health system reform,— Nielsen said in a statement. “We are hard at work to ensure that seniors have continued access to health care, and the President’s budget took an important step toward achieving that goal by including $329 billion to stop Medicare physician payment cuts.—

A high-level AFL-CIO official also is expected to attend, as is National Federation of Independent Business President Dan Danner and former Democratic-turned-GOP House Member Billy Tauzin (La.), now president of the Pharmaceutical Research and Manufacturers of America.

One group that confirmed it was not visiting 1600 Pennsylvania Ave. today is the Association of American Physicians and Surgeons, which represents doctors in private practice.

But Katheryn Serkes, director of policy and public affairs, says this isn’t the first time the group has been snubbed.

“It’s really interesting because this just feels like 1993 all over again with the secret meetings of the Clinton administration,— she said. “I don’t even see the point. Apparently the transparency doesn’t include people who might have a little bit of a different point of view.—

Serkes says she knows of several “free-market solution groups— that were not invited, including the National Taxpayers Union and Americans for Tax Reform, a group run by conservative activist Grover Norquist.

“I mean how much is going to come out of this?— she angrily asked. “It’s nice to be asked to the dance, but dances aren’t what life is about. It’s about making policy change that is meaningful.—

A health care lobbyist, however, said Wednesday that uninvited groups shouldn’t sulk, downplaying the meeting’s significance and agreeing it was little more than an dog-and-pony show. The real work, the lobbyist said, would be in coming weeks when Congress begins determining which industries might be winners and losers.

And even though Obama’s proposal calls for drug companies, insurance providers, physicians, hospitals and medical-device makers all to take one for the team, lawmakers may see it differently, the lobbyist said.

“I don’t get the sense that a lot of people are upset because the president’s budget and the summit are clearly not intended to be hard-and-fast, this-is-where-we-are-on-health-care-reform,— the lobbyist said.

Today’s summit, he added, “will be a little more specific than the president’s budget, but they’re not going to put out a comprehensive plan … until we see a legislative proposal. It’s hard to distill it down.—