Amid a lengthy battle with cancer, Los Angeles Area Chamber of Commerce President and Chief Executive Rusty Hammer announced his resignation Thursday.

Hammer, 51, said that his two-year battle with a rare form of leukemia has left him unable to return to work full-time and that he is stepping down to allow for a replacement. He will remain president and chief executive until that replacement is found.

“I have tried to the best of my ability to stay in touch as president and CEO, but frankly, what I’ve discovered is that it’s very difficult for me to predict with certainty when I’ll be able to return in a full-time mode,” Hammer said Thursday from his hospital room.

Hammer, who took over as CEO of the chamber in October 2001, helped restore some of the organization’s luster after a prolonged membership decline. Member rolls grew and the chamber assumed a much higher political profile, endorsing candidates, setting up a transportation coalition and a network of local chambers.

Then, in the summer of 2003, came the leukemia diagnosis. After a long hospital stay, Hammer was able to work from home on a part-time basis last year. But he suffered several relapses as well as complications from the cancer treatments. Many of his duties had to be assumed by chamber board chairmen George Kieffer and Chris Martin.

Earlier this year, Hammer said he made significant progress and had managed to stay out of the hospital for three months. “I had a good streak going and thought that by this fall, I would be back full-time,” he said.

But another relapse convinced him he had to step down.

Chamber spokeswoman Marie Condron said the board will launch a nationwide search for Hammer’s replacement.