A new national arts coalition will be announced today, and it has several answers to the question: "Why another arts group?"

"First, we hope this is the beginning of a Brookings Institution for the Arts," says James Backas, the executive director of the American Arts Alliance.

In addition to the fact-finding research mission - sporadically done by professional pollsters now - the alliance will be an advocate's voice and lobbyist for the arts to Congress and the White House. And its concerns will be wider than getting more federal money for the arts.

"Laergy, tax reform, social security - all these are important to the arts. The last thing we want to be thought of is as a group seeking only more federal grants," Backas says.

The performing arts have to live in the real world of taxes, energy conservation, and other everyday concerns, he points out. Traditionally, arts advocates have spoken up only when the authorization and appropriations requests for the National Endowment for the Arts have come up before special subcommittees.

But arts groups also should be making their case on other legislation such as tax reform and energy policy. Backas argues, before such powerful committees as House Ways and Means and Senate Finance.

As an example, he points to the provision, killed by the House on Wednesday, that would have required mandatory Social Security coverage for employees of non-profit institutions as well as federal government employees.

"It isn't that we are against Social Security coverage. But the congressmen hadn't thought out what it could mean for the arts and were surprised when we pointed it out," Backas says.

The problem for the performing arts is that many musicians, singers, and dancers do not have a primary employer and operate like individual entrepreneurs.

An opera star who commands $6,000 a performance might fulfill the $16,500 base for Social Security taxes in January with one opera company. But when she appears with other opera companies, each would start over again in paying the employer's matching levy.

"We asked the Houston Opera Company to do a quick estimate for us. They found it could cost them $150,000 a year if they did. That's enough to worry about," Backas says.

Energy costs and conservation also are important to arts groups. The new alliance will be telling legislators about the need for humidity controls in museums and for dance groups to tour for performances before a rapidly growing audience. There is also a need, Backas points out, for research on fuel conservation and conversion in the "old, beautiful buildings" that house museums, theaters, and opera companies.

The American Arts Alliance is a coalition of 420 non-profit professional groups - theater companies, symphony orchestras, Museums, dance troupes.

There already are several other arts coalitions, including the American Council for the Arts, renamed from the Associated Councils for the Arts. It represents primarily state and community arts councils.

The American Arts Alliance, with a first-year budget of $200,000, a staff of four, and an office on Capital Hill, is supported by a percentage levy on members.They are drawn from five service organizations: Opera America, Theater Communications Group, Association of Art Museum Directors, American Symphony Orchestra League, and American Association of Dance Groups.

Backas, once a professional clarinetist, taught music history at Peabody Conservatory and served six years as director of the Maryland State Arts Council.

He says one mission of the arts allianc will be to press for the formulation of a national policy on the arts. He described the organization as "supportive" of Livingston Biddle, who was nominated by President Carter as head of the Endowment for the Arts.