Still tied in polls as the final hours elapsed before Election Day, gubernatorial hopefuls W. Mitt Romney and Shannon P. O’Brien raced through the state yesterday, towing their parties’ top stars in last-ditch efforts to gain the edge before the final reckoning in voting booths.

Polls in just the last few days have indicated that Republican Romney’s popularity has surged, eradicating Democrat O’Brien’s slight lead in polls taken less than a week ago.

A survey released yesterday by Suffolk University and WHDH-TV found Romney has gained a four-point advantage, although that was still within the poll’s margin for error.

Two separate weekend polls showed a similar trend. A Boston Globe/WBZ poll published Sunday gave Romney an edge, 40 to 38 percent, while a Boston Herald poll published the same day gave O’Brien a mere 42 to 41 edge, down five points from a Herald poll published five days earlier.

Pollsters speculated that O’Brien’s late slip was tied to her performance in the final debate last Tuesday. Some observers said her performance had come off as too aggressive.

Keeping up the campaign’s hostile tone through the bitter end, Romney and O’Brien both released last-minute attack ads within the past several days—while they continued to blame each other for the negative tone.

The election will be the most expensive in state history, with $25 million spent through October—and Secretary of State William F. Galvin estimated yesterday that an “obscene” $50 million has been spent, all told.

But despite all the money spent, neither candidate has been able to pull ahead—so yesterday, each turned out old-fashioned major star power in their final push.

Last night in the North End, Romney rallied with former New York Mayor Rudolph W. Giuliani. (Please see front-page story.)

“Ultimately, it comes down to who’s going to be the better leader,” Giuliani told the crowd. “This man is a leader all throughout the country. The stature that he brings to this office will help this state.”

Romney also campaigned yesterday at a Reebok factory in Canton.

“This is a campaign about jobs,” he told workers there. “I’m the only candidate in this race who’s spent his time trying to create new jobs.... I’ll make it my highest priority.”

Meanwhile, Democratic heavyweights Sen. Edward M. “Ted” Kennedy ’54-’56 and former President Bill Clinton rallied with their candidate.

Kennedy made a rare appearance in political advertising this weekend when he appeared in an O’Brien commercial and he stumped statewide with her on Sunday. Clinton made a brief rally appearance yesterday on his whirlwind tour of political battlegrounds in the Northeast.

In the elections’ final days, attention has zeroed in on Green Party candidate Jill E. Stein ’72-’73, who has held a steady five percent in polls—enough to sway the election one way or the other.

“Don’t you be Nader-ed again,” Clinton told an O’Brien rally in downtown New Bedford yesterday.

And in a Sunday night rally, U.S. Rep. Barney Frank ’61 joined with two of O’Brien’s opponents in this fall’s Democratic primary, Robert B. Reich and Warren Tolman, in urging progressives to vote O’Brien.

But the Stein campaign was unfazed.

“The only way they will develop an agenda that’s progressive is if we vote Green,” Stein told supporters in a rally held last night on Harvard’s campus. (Please see front page story.)

For a dozen years, liberal Massachusetts has elected a Republican governor—a trend that local political observer Robert Winters sees as an effort to balance the powers of the overwhelmingly democratic state legislature.

“The concept of having a fiscal conservative, i.e. a Republican, as governor, will appeal to people,” Winters said.

At stop after stop, both Romney and O’Brien invoked the debacles of Massachusetts governors from days gone by. At his campaign stops, Romney told crowds that during the term of Michael Dukakis—the state’s last Democratic governor—“the economy sank deeper into recession.”

Meanwhile, O’Brien released two ads playing on polling data that shows that voters think her running mate, Chris F. Gabrieli ’81, is better prepared to be governor than Kerry Healey ’82, Romney’s No. 2. Her ads point out that two recent Massachusetts governors have departed early from the Corner Office, leaving the state in their lieutenant governors’ hands.

“We’ve seen how important the lieutenant governor can be,” the ad says, alluding to the early departures of William F. Weld ’66 and A. Paul Cellucci.

Weekend polling also revealed that about ten percent of the state’s voters are still undecided, which makes winning over the vast population of unaffiliated voters even more important for the leading contenders.

While there are nearly three times as many registered Democratic voters as Republicans in the state, there are almost as many unenrolled voters (registered voters not affiliated with a political party) as Republicans and Democrats put together.

All of the local competitive races in Cambridge were settled in September—on the day of the Democratic primaries.

Only one Cambridge state representative, Timothy J. Toomey of East Cambridge, faces a challenge. For the first time in eight years, Toomey will not be on the ballot alone, although local political observer Robert Winters says the challenge from Green Party candidate Paul Lachelier amounts to running unopposed.

—Staff writer Lauren R. Dorgan can be reached at dorgan@fas.harvard.edu.