Elizabeth Warren making Senate candidacy official Wednesday

After a brief flirtation with the race, consumer advocate Elizabeth Warren plans to officially become a candidate for Senate in Massachusetts on Wednesday, giving Democrats a candidate with national stature in the rare contest where they are on offense in 2012.

Warren oversaw the launch of the new Consumer Financial Protection Bureau before leaving the Obama administration this summer. She formed an exploratory committee for the race shortly after.

“The pressures on middle-class families are worse than ever, but it is the big corporations that get their way in Washington. I want to change that,” Warren said in a statement.

Democrats have been eager to field a top-flight challenger to Republican Sen. Scott Brown, whose 2010 special election victory for the seat once held by Ted Kennedy shocked the political world.

Warren comes into the race with the strong support of national progressives. The Progressive Change Campaign Committee has raised $130,000 through its “Draft Warren” effort. But as a first-time campaigner she will have much to prove in a race against Brown, who has quickly become the Bay State’s most popular politician, according to various polls.

Democrats are eager to avoid a repeat of the Martha Coakley fiasco; the state attorney general ran a widely panned campaign in that 2010 race, famously dismissing Brown’s efforts shaking hands with voters outside Fenway Park.

Warren will immediately begin a retail campaign, greeting commuters in Boston on Wednesday morning before traveling to other cities as part of her launch.

“I will work my heart out to earn the trust of the people of Massachusetts,” Warren said.

Democrats are facing an uphill climb in the effort to maintain control of the Senate after 2012, playing defense in 23 of the 33 seats up for election next fall (including two independents who caucus with the party). Six of those 23 will be open seats.

Massachusetts is at the top of the Democratic Senate Campaign Committee’s “Six for ‘12” list of GOP-held seats they plan to aggressively target.