Former Sen. Dan Coats (R) on Wednesday stopped short of formally announcing a campaign against Sen. Evan Bayh (D) but said he would take steps to prepare for a race.

“After much thoughtful consideration, I have authorized my supporters to begin gathering signatures as I test the waters for a potential challenge to Evan Bayh in 2010,” Coats said in a statement Wednesday afternoon. “Over the next few weeks, I will be talking to Hoosiers from all walks of life, and I will make a formal announcement regarding my intentions in the near future.”

Coats represented northeastern Indiana in the House from 1981 to 1988, when he was appointed to the Senate to succeed Dan Quayle after his election as vice president. Coats served in the Senate for 10 years and was succeeded by Bayh, who is running for a third term this year.

As news of Coats’ plans spread Wednesday, influential Republicans began lining up behind the former Senator, and Democrats began launching attacks.

Rep. Mike Pence (R), who had considered challenging Bayh, released a statement on Coats, promising, “If he runs, I will support him.”

In a sign that Democrats are concerned about having another seat put into play this year, the Democratic Senatorial Campaign Committee released a statement attacking Coats as a “federally registered lobbyist whose client lists include banks, private equity firms, and defense contractors.”

Coats would become the instant frontrunner in a May 4 Republican primary that already has four candidates, including former Rep. John Hostettler and state Sen. Marlin Stutzman.

Coats, now a senior adviser with the firm King & Spalding, has about two weeks to collect the signatures of 4,500 Indiana voters, including at least 500 in each of the state’s nine Congressional districts.