Updated: 3:33 p.m.

Arkansas state Sen. Gilbert Baker (R), who has been openly contemplating a Senate bid for nearly six months, announced Tuesday that he will challenge Sen. Blanche Lincoln (D) in 2010.

“I believe that Arkansas’ next United States Senator should help provide checks and balances on the policies being pushed by President [Barack] Obama and the D.C. leadership,— Baker said in his announcement Tuesday afternoon.

Baker’s decision comes a week after a poll was released by a Democratic firm that showed Baker beating Lincoln in a hypothetical head-to-head race. That poll by the North Carolina-based Public Policy Polling also showed Lincoln with just a 36 percent approval rating, with 44 percent of voters disapproving of the job she’s doing.

Baker, who is one of the most senior members of the state Senate, is joining a crowded GOP primary field that now includes six candidates — and is without an obvious frontrunner.

“I look forward to a spirited primary campaign and a vigorous debate about the many issues facing Arkansas,— Baker said.

According to the announcement, Baker will spend the month of September traveling the state and developing a campaign and plans to hold a formal campaign kickoff in October.

The National Republican Senatorial Committee hailed Baker’s entry into the race.

“Today’s announcement by Gilbert Baker is another indication that Blanche Lincoln is facing an uphill battle in her quest for re-election in 2010,” said Amber Wilkinson, an NRSC spokeswoman.