TWO Broadway shows have hit snags on the way to their opening nights.”The Wild Party,” the new musical by Michael John LaChiusa, was forced to cancel Thursday’s preview performance when its star, Mandy Patinkin, was put on vocal rest by his doctor.

Late yesterday afternoon, a publicist for “The Wild Party” said performances would resume last night, with David Masenheimer filling in for the ailing Patinkin until further notice.

There were also behind-the-scenes rumblings that Patinkin’s vocal problems would force the producers of “The Wild Party” to postpone the opening night, now slated for April 13.

The musical is running nearly 2½ hours without an intermission. Audiences have been complaining about the punishing length, while director George C. Wolfe is trying to shave at least a half-hour off the running time, production sources said.

Trying to do that without Patinkin on hand will be difficult.

But as of yesterday, “The Wild Party” was sticking to the April 13 opening, its publicist said.

The other show that ran into trouble Thursday night was the revival of “A Moon for the Misbegotten.”

During a performance attended by drama critics from the major newspapers, a man who’d had too much to drink laughed “wildly” during the first act and sobbed “loudly” during the second, one critic said.

Then, when someone asked him to be quiet, the inebriated theatergoer started punching the people around him.

The police were called in to break up the brawl.

The critics were invited to see the show again last night.

“Moon” opens tomorrow.