Baker vs. Patrick, with the state's future on the line.

Republican Charles D. Baker Jr. officially entered the governor’s race yesterday, filing his paperwork with the state and then swiftly launching into an attack on Governor Deval Patrick’s handling of the budget and economy.

Baker immediately pledged not to raise taxes and said he would try to repeal the recent increase in the state sales tax, which will go from 5 percent to 6.25 percent Saturday, if he is elected.

“I’m a no-new-taxes candidate,’’ he said, adding later for the television cameras: “Yeah, read my lips: No new taxes.’’

Patrick, who signed the sales tax increase last month, dismissed Baker’s criticism.

“That’s a message that is stuck in the past, that is stuck in rhetoric,’’ Patrick told reporters yesterday afternoon. “I mean, there’s a campaign coming, but right now, I’m having to make these decisions, and I keep meeting people who actually want the schools to be funded, who actually want our healthcare experiment to succeed.’’

Baker’s candidacy, which he informally announced earlier this month, jump- starts the 2010 campaign as Patrick faces low poll numbers and declining state revenues. Baker will be running for the Republican nomination against Christy Mihos, a former member of the Turnpike Authority board who ran against Patrick three years ago as an independent. State Treasurer Timothy P. Cahill, who left the Democratic Party July 8, is weighing a run as an independent.

Baker, who announced the same day that he would resign as chief executive of Harvard Pilgrim Health Care, is seen by many of the party faithful as the leading Republican challenger, but he is largely unknown outside political and business circles.

He seemed comfortable in the spotlight yesterday, with a ready smile, several jokes, and light banter with reporters during a 19-minute press conference.

As he walked into the state’s Office of Campaign and Political Finance to file his papers, he was greeted by about a dozen supporters carrying signs. A campaign worker filmed the process for Baker’s new website, www.charliebaker2010.com.

But Baker’s background in finance, which can make him seem wonkish, was also on full display as he spoke of the state’s unfunded pension liability and a financial instrument known as a swaption. He mentioned the state’s “structural deficit’’ at least four times during the first 2 1/2 minutes of the press conference.

It was clear, on Baker’s first formal day in the race, that Patrick’s financial stewardship will be a central issue in the campaign.

“I think he let the budget get away from him, and once the budget gets away from you, really bad things happen,’’ Baker said.

When asked what needs to be cut from the budget, Baker said that “everything should be on the table,’’ including scaling back the state’s landmark healthcare initiative.

“I would start with a head count,’’ Baker said. “We have cities and towns that are laying off and furloughing people all over the place and we don’t even have a hiring freeze in place at the state level.’’

Even before the press conference, Democrats pounced on Baker’s candidacy. Lieutenant Governor Timothy P. Murray released a statement saying that the Republican is “nothing more than an overcompensated insurance executive who placed profits over patients at the expense of hard-working families and employers in Massachusetts.’’

Murray also criticized Baker’s involvement in the financing of the $15 billion Big Dig, saying, “if you look up crisis in the dictionary, you’ll find a picture of Baker and a narrative on the Big Dig financing scheme.’’

Baker sought to distance himself from the project yesterday, calling it a “bipartisan headache.’’

“I do think it’s kind of ironic that I’m being criticized for my small role in the Big Dig, when one of its chief architects and enablers is the transportation czar for the current administration,’’ Baker said.

Patrick’s transportation secretary, James A. Aloisi Jr., is a former general counsel for the Turnpike Authority and drafted the legislation that put the authority in charge of the Big Dig.

It was also clear yesterday that Baker is attempting to position himself as the kind of Massachusetts Republican voters have favored in the past: fiscally conservative, but socially moderate.

Baker said he supports abortion rights and same-sex marriage, adding: “My brother’s gay, and he’s married, and he lives in Massachusetts, so I’m for it. Is that straight enough?’’

He also said he supports the death penalty, which puts him at odds with Patrick.

Baker attempted to distance himself from the national Republican Party, although he would not rule out taking money from the party.

“I’m not going to participate in national discussions and national politics; I’m interested in what happens here in Massachusetts,’’ he said.

UPDATE: More from Scott Helman, Hillary Chabot, WBZ-TV, the New York Times, NECN and Joan Vennochi.

SECOND UPDATE: From Howie Carr and Mary Connaughton.