FANS of Whitney Houston were a little concerned after her concert at Caesars Palace in Atlantic City Saturday night. Despite rumors of drug use and other personal problems, die-hard fans came out in droves to support the diva. But instead of being treated to hours of her hits, the audience got one surprise after another. "She stopped in the middle of eight or nine songs. She either forgot the words or her voice cracked and then she ended up doing all these weird cover songs - not any of her hits," one spy complained. Houston stopped in the middle of "I Wanna Dance With Somebody (Who Loves Me)," apologized to  the crowd and said, "I want to make it up to you guys" - and launched into  "The Star-Spangled Banner." Later, she got six words into "I Will Always Love You" when her voice cracked. "I'm not singing this song. My voice isn't up to it," she announced before diving into "American Pie." On Tuesday, Whitney sang at a Fourth of July bash at Cablevision honcho Charles Dolan's house in Oyster Bay attended by Gov. Pataki and featuring a high-kicking performance by the Rockettes. But the diva had to cut her set short when the power went dead after four songs. Houston's rep didn't return calls.