SPRINGFIELD (AP) -- U.S. Rep. Stephen Lynch launched his bid for the U.S. Senate on Thursday casting himself as a "bread and butter" Democrat who learned firsthand how government can offer a hand up in hard times.

Lynch capped a daylong tour of Massachusetts, including stops in Springfield and Worcester, with a rally at a packed iron workers union hall in the blue collar neighborhood of South Boston, where Lynch grew up and worked as an iron worker for 18 years before entering politics.

"I know what it's like to stand in an unemployment line," Lynch said to hundreds of supporters. "I learned that in severe economic downturns, that sometimes the only force that can correct that inequity, or give people a chance to lift themselves out of difficulty, or provide some temporary relief, is the government."

Lynch also criticized efforts to line up Democratic support for U.S. Rep. Edward Markey, who is also seeking the party's nomination for the special election to succeed Sen. John Kerry.

Lynch's announcement guarantees a Democratic primary.

Kerry, who will be sworn in as secretary of state today, is among those supporting Markey, who also starts the race with a substantial financial advantage -- $3.1 million in his campaign account compared to Lynch's $740,000 as of the most recent campaign finance reports.

Markey welcomed Lynch to the race even as he portrayed himself as the better heir to Kerry's legacy.

"We need a senator who continues to stand up for the progressive values that John Kerry and Massachusetts believe in and who's focused on creating the jobs our economy needs," Markey said in a written statement.

Lynch, accompanied by some union supporters, and mingling among the breakfast regulars at O'Brien's Corner restaurant in Springfield, touted himself as the underdog outsider and portrayed Markey, the dean of the state's congressional delegation, as "a creature of the Democratic establishment in Washington D.C."