He was the querulous balladeer in Stephen Sondheim's Assassins; now actor Patrick Cassidy grabs a gun as Tom Wopat's replacement in Broadway's Annie Get Your Gun, beginning Sept. 6.

Cassidy will play Frank Butler opposite Cheryl Ladd, who is taking Bernadette Peters' role as Annie Oakley, also starting Sept. 6.

In the classic Irving Berlin tuner, in revival at the Marquis Theatre, Frank and Annie are rival sharpshooters wrestling with the egos and affections. "Anything You Can Do," "An Old Fashioned Wedding" and "My Defenses Are Down" are part of the hit-filled score.

Cassidy is the son of Jack Cassidy and Shirley Jones, and starred on Broadway in Leader of the Pack and The Pirates of Penzance, and has appeared in Three Penny Opera, Company, Martin Guerre, The End of the Day and the world premiere of Assassins at Playwright Horizons.

Annie Get Your Gun won the 1999 Best Revival (Musical) Tony Award. Graciela Daniele directed and co choreographed (with Jeff Calhoun). Barry and Fran Weissler are producers. Wopat and Peters exit the show Sept. 2. There are no performance Sept. 3 5.

For ticket information, call (212) 307-4100.