BOSTON — Seeking to broaden his appeal as a presidential candidate beyond those Republicans attracted by his reputation as a social conservative, Governor Romney is making a play for economic conservatives by focusing on taxes.

Moments before Mr. Romney, whose term as governor ended this week, entered the offices of his presidential exploratory committee for the first time as a private citizen, he warned that the new Democratic Congress would succumb to raising taxes.

“The Democratic agenda seems to be surrounding the idea of raising taxes and more government spending, and more taxing is not good for the American people, it’s not good for the economy, it’s not good for America,” Mr. Romney said. “I think you’ll see the Republicans in both houses and in the White House stand firm. Holding the line on taxes is critical to strength of our economy and the well-being of the American people.”

Mr. Romney’s comments come fresh on the heels of the news that he signed the “Taxpayer Protection Pledge” promulgated by Grover Norquist, the president of Americans for Tax Reform. Mr. Romney distributed an image of the pledge signed by himself and two witnesses, dated January 3. It is a promise that he will “oppose any and all efforts to increase the marginal income tax rates for individuals and/or businesses.” It adds that he will also “oppose any net reduction or elimination of deductions and credits unless matched dollar for dollar by further reducing tax rates.”

Senator Brownback of Kansas, another prospective presidential candidate, also signed the pledge, according to the Americans for Tax Reform Web site, atr.org. Messrs. Romney and Brownback join President Bush, 43 senators and 197 members of the House, the group said. “By signing the Pledge, Sam Brownback and Mitt Romney demonstrate allegiance to hardworking taxpayers nationwide,” Mr. Norquist said in a statement. “It is now up to other candidates in the race to stand up to the challenge.” ATR’s Web site lists Messrs. Romney, Brownback and Illinois Republican activist John Cox under a heading Presidential Campaigns 2008.

Mr. Romney “is the first major candidate to sign it,” Mr. Norquist said. “Giuliani has not signed the pledge for 2008, nor has McCain. I do expect both of them to do so.”

Mr. Romney did not sign a similar pledge during the 2002 campaign for governor in Massachusetts. The executive director of Citizens for Limited Taxation, Barbara Anderson, said Mr. Romney did, however, vow, not to raise taxes during that contest. “He said, ‘I’m not going to raise taxes, but I’m not going to sign anything,'” Ms. Anderson said. “He made it verbally, and he kept it.”

The executive director of the Beacon Hill Institute, a fiscally conservative research institute based at Suffolk University, David Tuerck, gave Mr. Romney high marks for his fiscal record. “I would give him an A-,” Mr. Tuerck said. “He held the line on income tax and the sales tax.”

In other developments, Mr. Romney is stepping up his fundraising efforts. His exploratory campaign announced a group of nine finance co-chairmen, six of them previously either Bush/Cheney ’04 Pioneers or Rangers. The fund-raisers are Christopher Collins, managing member of First Atlantic Capital; Mark Guzzetta, president of Gemstone Development; Jon Huntsman Sr., chairman of the Huntsman Corp.; John Miller, founding member of National Beef Packing Co.; John Rakolta Jr., chairman and CEO of Walbridge Aldinger; Ambassador Mel Sembler; Tom Tellefsen, president of Tellefsen Investments; Ted Welch, owner of Ted Welch Investments, and Meg Whitman, president and CEO of eBay. Both Mr. Sembler and Mr. Welch are former national finance chairmen for the Republican National Committee. Unlike Mr. Giuliani who is organizing his fund-raising effort around All-Stars who raise $100,00 and MVPs who raise $200,000, Mr. Romney is sticking with the fundraising lingo of Mr. Bush, pioneers and rangers.

Tanned and relaxed for a candidate about to embark on the most arduous political test any politician can face, Mr. Romney said he was optimistic about his fundraising prospects. “Not having raised a dollar for a presidential exploratory committee, it’s a little hard to predict what exactly our figures are going to look like,” Mr. Romney said. “We’ll be able to raise sufficient funds to mount a very competitive campaign.”