"I believe that this is in the best interest of our state, as it will allow the Republican party's best chance of holding the governor's office in November," Swift said, her voice choking with emotion.

The announcement of Romney's entrance into the GOP race for governor had been anticipated for weeks, and Swift's popularity suffered with each poll taken. Still, until recently, she said she welcomed a challenging campaign. Many of her staff did not know until Tuesday about her decision.

"It is rare in Massachusetts politics that people are stunned," said Michael Goldman, a longtime Democratic activist. "This is a genuinely stunning event."

Swift's announcement stole the thunder of Romney, who scrapped plans to make his formal announcement with supporters at a Boston hotel and instead held a subdued news conference in front of his Belmont home. He thanked Swift for her years of work and said he didn't want to take the attention away from her, for this day.

"It's admirable that she's decided to focus her resources on managing the state during tough economic times and also to help raise her family with all her energy and heart," Romney said, surrounded by his wife Ann, three of his five sons, three daughters-in-law, and two grandchildren.

But Romney, whose father George Romney was governor of Michigan, was quick to add: "Lest there be any doubt, I'm in. The bumper stickers are printed, the Web site's going up. The papers are going in today."

A Boston Herald poll on Sunday showed Romney, whose only political experience is an unsuccessful challenge to Democratic Sen. Edward Kennedy in 1994, leading Swift 75 percent to 12 percent.

Swift's decision to drop out of the race to spend more time with her husband and three young daughters dramatically changes the complexion of the governor's race, which features five Democrats vying for the nomination. Now, they'll have to campaign against each other, and against Romney.

Democrats include: Senate President Thomas Birmingham, former U.S. Labor Secretary Robert Reich, state Treasurer Shannon O'Brien, former state Sen. Warren Tolman and Steve Grossman, a former national Democratic Committee chairman.

Swift, who has been plagued by personal and political controversies, said she decided not to take on the simultaneous task of being a mother of three, running for election and governing during a budget crunch.

"Having said early on the time with family was non-negotiable, something had to give," Swift said. She plans to serve out her term until the end of the year.

Within moments of making his announcement, Romney was challenged on his stand on abortion, a hot-button issue in a state that in the last three elections has supported fiscally conservative, socially progressive governors.

"On a personal basis, I don't favor abortion," he said. "However, as governor of the commonwealth, I will protect the right of a woman to choose under the laws of the country and the laws of the commonwealth."

Swift, 37, became Massachusetts' first female chief executive, and the nation's youngest, in April, succeeding Paul Cellucci when he became ambassador to Canada. She was the first governor in the nation's history to give birth in office when she had twin girls in May. She also has a 3-year-old daughter.

Swift said she did not know what she planned to do next, but told reporters, "You guys keep telling me I'm young."

White House spokesman Ari Fleischer said no one from the Bush administration urged Swift to drop out. Swift said she would not take a federal job.

The birth of Swift's twins produced favorable national publicity and a bounce in the polls. But when she returned to work at the end of June, she continued to find herself with little political capital and a Statehouse dominated by Democrats.

That made tough challenges even tougher: a worsening budget crunch, calls for added security measures after Sept. 11, and a controversial decision not to commute the sentence of a convicted child molester.

Earlier, when she was lieutenant governor, the state Ethics Commission ruled she had created an appearance of impropriety by allowing aides to baby-sit for her older daughter and fined her $1,250.

More recently, she was sued by two members of the Turnpike Authority board whom she fired after they voted to delay toll hikes.

Romney has been riding a wave of popularity since successfully leading the Winter Olympics. A longtime Massachusetts resident who graduated from Brigham Young University in Utah and sent his children there, Romney graduated from Harvard Business School and went to work in Boston at Bain & Co., where he rose to chairman.

In 1984, he co-founded Bain Capital, a venture capital company. He has been active in Belmont's Mormon community, which constructed a 70,000-square-foot temple in 2000.

Romney, who returned to Massachusetts on Sunday from Utah, has said he considered the health of his wife, who has multiple sclerosis, before deciding to run. Ann Romney said Tuesday she was feeling healthy and was s fully behind her husband's candidacy. When asked about her preference in the decision, however, she paused and said: "Mitt and I would have loved to have a few weeks off." (AP)