WASHINGTON (Reuters) - U.S. congressional leaders are giving up on broad immigration legislation that would legalize millions of illegal immigrants and instead will concentrate on border security ahead of the elections, Senate Majority Leader Bill Frist said on Wednesday.

"I think it would be next to impossible to pass a comprehensive bill that includes dealing with the diversity of 12 million people here in the next three weeks," the Tennessee Republican told reporters.

President George W. Bush backs comprehensive immigration legislation along the lines passed by the U.S. Senate. That bill would have created a guest worker program and put millions of illegal immigrants on a path toward U.S. citizenship.