"Crossed Swords." a tedious movie version of "The Prince and the Pauber," may earn a footnote in movie history by becoming the last attraction at Radio City Music Hall. The Music Hall's economic problems may be insoluble. After all the second most popular release of 1977, "Smokey and the Bandit." did only moderate business when it played exclusively there.

Still a succession of clunkers like "Crossed Swords." supposedly intended for family audiences but produced with little discernible flair, no doubt hastened the theater's decline.

Insipid comedies, boring nature studies and ponderous adventure melodramas have depressed the family market because they were presumed to be the only thing suitable for general consumption. The presence of a new costume picture as beautiful and emotionally charged as "The Duellists" makes "Crossed Swords" look like a bad joke. Since it's content to perpetuate all the stilted unimaginative traditions that "That Duellists" transcends.

"The Prince and the Pauper" has never impressed me as more than one of Mark Twain's less inspired historical whimsies. But 1937 Warners production did serve as a pleasant warm-up for many of the people who collaborated on "The Adventures of Robin Hood" the following year - Errol Flynn, Claude Rains, Alan Hale, director William Keighley, composer Erich Wolfgang Korngold.

This new adaptaion is closer to stale leftovers.

Warners cast twin boys as the young lookalike heros who exchange identities and roles: the commoner Tom Canty and Prince Edward. The son of Henry VIII. whose death in the course of the story threatens to elevate poor ill-prepared Tom to the English throne. "Crossed Swords" suffers from the peculiarly insipid presence of Mark Lester in a dual role. Lester has grown out of the quality of pretty bewilderment that made him so touching as a child performer. He's evolved into a birdlike adolescent - sort of Marcel Marceau as a young stork - with a painfully amateurish acting style.

Movies this stilted usually separate the actors who can hold their own from the ones who desperately need directorial help. Oliver Reed. Rex Harrison and George C. Scott are in no need here. Although neediest case, Raquel Welch runs him a close second in an irresistibly funny bit role, which requires her to heave her chest and keep her mouth hanging open for several minutes before she speaks a line.

Charlton Heston, a mild hoot as King Henry, seems to have the worst dialogue until David Hemmings shows up as the villain. Heston's choicest, spoken with his foot on Lester as Tom: "Wiggle-worIs the weight of England too heavy for you? I've borne it for these five-and-thirty years."

Hemmings' choicest, aimed at Lester as Edward: "Give this noisy whelp a taste of your whip."

Richard Fleischer directs with the imperturbable mediocrity that seems to have become his specialty from "Dr. Doolittle" through "Mandingo." however, he seems more inclined to break the prevailing narrative monotony with prolonged sluggish matches rather than swordplay. "Crossed Clubs" or "Clenched Fists" would be much more appropriate titles.