A New York federal court has granted the country's largest theatrical production organization, the Shubert Organization in New York, the right to manage and book Washington's National Theatre indefinitely.

The Shubert's bid to run the National was strongly contested by the New York-based Nederlander Corp., the nation's second largest theatrical organization, generally regarded as the Shubert's main rival. The Nederlanders had filed papers in court arguing that a Shubert-run National Theatre would be in violation of antitrust laws and restrict competition.

The Shubert Organization is barred from acquiring an interest in any additional theaters by a 1956 consent decree. When the group wants to acquire a new theater, it must go to court to get the decree amended. This spring, the New York court had ruled that the Shubert group could manage the National only on an interim basis through the summer of 1981.

"I could not be more delighted with the opinion or the language it is expressed in," Shubert head Gerald Schoenfeld said yesterday, after first hearing of Wednesday's decision by federal district court Judge Morris Lasker. "I think [the Nederlanders' objections] were ill-founded."

Lasker said in his opinion that the Shubert's running of the National "will not restrain competition." Lasker noted that the Department of Justice antitrust division had submitted a memo saying that "granting the application would foster rather than restrain competition."

The Nederlanders had argued that the Shubert's move to the National would "restrain competition on a nationwide basis." Lasker's opinion says "the record demonstrates the arguments are without merit."

"Naturally I'm disappointed, but I don't think I should comment until I've seen the opinion," Nederlander attorney Jonathan Weisgall said yesterday.

During this latest feud between the tow rivals, the Shubert Organization had ceased giving Nederlander officials the customary "house-seat" privileges at Shubert theaters. "We are not restoring them," said Schoenfeld. "House-seat privileges connote the extension of a courtesy. We are not extending any courtesies, nor are we asking for any."