Make no mistake about it, classical music is a business; not like auto making, but a business nonetheless. And because that business has changed substantially in the past generation, reins that the Justice Department placed on the biggest agents in the field in 1955 have now been removed.

There's more glitter involved in handling world-class singers, conductors and instrumentalists than in manufacturing mundane industrial products. But the story behind the June cancellation of the consent decrees on Columbia Artists Management Inc. is typical of the way the Reagan administration antitrusters have been reexamining existing consent decrees and working with former adversaries in getting off the books decrees no longer relevant.

Where it was once typical for the court orders ending antitrust cases to apply forever, now most have a life of only 10 years. The concert business of 1955 was very different from today's. Not only were there substantially fewer bookings overall, but for all but the biggest names and the biggest cities, those bookings were firmly in the hands of two agencies, CAMI and National Concert and Artists Corp. Each dominated the bookings in certain cities through local community concert groups. These groups put on subscription series and agreed to book only performers managed by the agency with which the groups were affiliated. It was virtually impossible to build a career without landing concerts with those associations.

Columbia booked for such groups in 800 towns and National had 400. Justice contended that each had agreed to stay out of the markets organized by the other. The government tried to open the market by forcing the management companies to give more freedom to their community concert groups, letting the locals book from any agent and making star names available to groups that do not book their entire season through a single agency. Since those rules went into effect, the concert business has gotten a lot more competitive -- but that change has almost nothing to do with the promises extracted by Justice.

The fact is, the independent management firms have shown only slight interest in trying to line up business from the community concert groups. What has happened since 1955 is an unforeseeable boom in the performing arts. There has been "a veritable explosion of the number of artists-management organizations serving the vastly increased concert market," said CAMI Chairman Ronald A. Wilford. "In the 30 years since entry of the decree, artistic opportunities for the concert artist have multiplied to the point where organized audiences constitute one of the lesser segments." Columbia has ties with only about 650 such groups now, and National is out of business.

Nonprofit arts groups, often funded by the National Endowment for the Arts or by state or city arts councils, are now putting on concerts, particularly those giving a leg up to young performers. At the other end of the spectrum, commercial producers who own their own theaters are booking big name classical performers into them, particularly ballet companies. The number of symphony orchestras in the United States has mushroomed, and the old-line philharmonic orchestras have extended their seasons; in all, they give some 25,000 concerts a year for which guest artists may be booked.

But the biggest change has been the shift at colleges and universities from occasional sponsors of concerts of limited appeal to big time impresarios, who put on music seasons that in many cities have taken over the role once filled by the community concert groups. About 450 schools have active programs of commercial concert booking; perhaps three-quarters of all professional concerts in the country now are put on by colleges and universities.

"Colleges and universities today constitute the single largest segment of the market for presentation of concert artists," the Justice Department said in papers urging the U.S. District Court in Manhattan to end the CAMI consent decree. The schools pay performing artists more than $150 million a year -- eight times the total paid by all symphony orchestras for soloists and guest conductors.

And the new generation of artist representatives that has grown up attuned to these new markets can give performers the assurance of a successful career that once only Columbia and National could award. The two together once made 80 percent of all the bookings for musical artists. CAMI still ranks as number one in the field.

But the smaller agencies have their quota of crowd pleasers, too. For instance: Rudolph Serkin has now chosen Herbert Barrett Management; Joan Sutherland and Richard Bonynge are with Colbert Artists Management, and Richard Stoltzman is represented by Frank Salomon Associates. In that changed environment, "access to community audience associations is not critical for independent managers," U.S. District Court Judge William C. Conner noted. He suggests that ending the consent decree may actually stimulate new competition.Moskowitz covers legal affairs for McGraw-Hill World News.