ST. PAUL — Former state Rep. Dan Severson is expected today to become the first Republican to wage a 2012 challenge to Minnesota’s Democratic U.S. Sen. Amy Klobuchar.

Severson, who served in the state House for four terms before his unsuccessful bid last fall for secretary of state, will announce his candidacy on the steps of the state Capitol, according to a consultant with direct knowledge of the plans. The consultant spoke on the condition of anonymity because he wasn’t authorized to discuss details ahead of the announcement.

Severson, 57, declined to comment on what he planned to announce.

The retired Navy pilot was the GOP’s nominee for secretary of state last year, attracting 928,000 votes — the second most for a Republican on the 2010 ticket — but well short of incumbent Democrat Mark Ritchie. Severson represented a St. Cloud-area district while in the Legislature.

Severson’s expected Senate bid would be the first GOP move in a race that many in the party have privately said would be difficult for Republicans.

Klobuchar won her seat in a 2006 blowout, and she’s maintained strong public approval ratings throughout her term. With more than $2.5 million in campaign cash as of mid-April, Klobuchar is trying to become Minnesota’s first incumbent senator to win re-election since 1996.

In January, Severson helped form the Minnesota Organization of Republican Veterans, which has a mission of recruiting and electing military veterans. Issues that Severson has supported include legislation that would require voters to show a government-issued photo identification card before getting a ballot.

Other Republicans have said they’re considering Senate campaigns, but none has taken a formal step.

R. Chris Barden, the Republican nominee for attorney general, said last month he was weighing a run. Bill Guidera, a News Corp. executive and officer for the state Republican Party, is “considering a run for U.S. Senate but needs to make sure the fundraising will be available,” said adviser Noah Rouen.

Last week, freshman state Sen. Dave Thompson of Lakeville said he would wait until after the legislative session ends to make his decision.

“Frankly, this was brought to me. I never talked about this and haven’t really until this point, until I started to get questions,“ Thompson said. ”I’ll just have to see what happens after we get our business taken care of here.“

Barring a special session, lawmakers are due to adjourn next Monday.