Giuliani, with 16 percent support, narrowly edged former Massachusetts governor Mitt Romney, currently seen as the party's front-runner because of name recognition and a large campaign warchest, with 15 percent.

Also polling high were former Alaska governor Sarah Palin with 13 percent, Texas Congressman Ron Paul, with 12 percent, and pizza magnate Herman Cain at 10 percent. Palin also is not a declared candidate for 2012 so far.

All other announced and potential candidates scored less than 10 percent support in a poll of 473 likely Republican voters conducted May 24-26. The margin of sampling error was plus or minus 3 percentage points.

source: Reuters