WASHINGTON (CNN) -- Sen. Chuck Hagel, a potential Republican presidential contender and an outspoken critic of the war in Iraq, will announce his "future plans" Monday at a news conference in his home state of Nebraska, aides said.

Hagel's advisers would not explicitly say the two-term senator will announce a bid for the GOP nomination at his Omaha news conference. But he plans to appear at a forum for presidential hopefuls put on by the International Association of Firefighters next week, the union announced
Wednesday, and he told CNN in January that he would make a decision about a
presidential run "soon."

Hagel, 60, was a decorated infantry sergeant in Vietnam. He supported the 2002 congressional resolution that authorized the invasion of Iraq the following year, but he has become an increasingly vocal critic of the Bush administration's handling of the war.

He called President Bush's plan to send thousands of additional U.S. troops to Iraq "the most dangerous foreign policy blunder in this country since Vietnam," and joined six other Republicans in February to back a non-binding resolution opposing the troop increase. The measure failed on a procedural vote.

"I believed what the administration said, that war would be a last resort," Hagel told Esquire magazine in a newly-published interview. "And the second thing is, at a critical time like this, the president needs a strong hand, and to some extent, you've got to trust him, until he lies or screws up or something."

Now, he told the magazine, Bush appears to believe he's no longer accountable, "which isn't totally true. You can impeach him, and before this is over, you might see calls for his impeachment. I don't know. It depends how this goes."

Despite his break with the party on Iraq, Hagel -- whose second term is up in 2008 -- has an otherwise-orthodox GOP voting record. He supported the Bush tax cuts in 2001, has a perfect score on abortion issues from the National Right to Life Committee and backed efforts to open part of Alaska's Arctic National Wildlife Refuge to oil exploration.

Polls suggest he will face an uphill battle in the GOP primaries, which have already drawn a crowded field.

A CNN/WMUR poll conducted in February found him trailing the pack among potential GOP voters in the first primary state of New Hampshire, drawing just 1 percent support.

A national poll, conducted by CNN for Opinion Research Corp. in mid-January, also put him at 1 percent among registered Republicans. By comparison, former New York Mayor Rudolph Giuliani led that survey at 32 percent, while Arizona Sen. John McCain -- Hagel's friend and frequent ally -- came in at 26 percent.