BOSTON, SEPT. 10 -- Fearing she would play the role of spoiler, Lt. Gov. Evelyn Murphy withdrew today from the Democratic campaign for governor, throwing the Massachusetts political scene into turmoil just eight days before the Sept. 18 primary.

The surprise announcement by Murphy, who had been trailing in a three-way race, raised the stakes for the remaining two candidates -- former state attorney general Francis X. Bellotti and John Silber, the on-leave president of Boston University. They are scheduled to face each other in a final debate Tuesday evening.

Murphy, who ran as an avowed liberal, promised to continue battling for "compassionate, effective government that meets human needs" and said she would vote for Bellotti, who is seen as the candidate most likely to gain from her abrupt departure.

As tearful supporters looked on in shock, Murphy made a brief statement at a Statehouse news conference and took no questions. She gave little reason for halting her stalled campaign, just three days after going for broke by taking charge as the state's acting governor and ordering spending cuts while Gov. Michael S. Dukakis (D), who is not seeking reelection, is in Europe on a trade mission.

"This is no time for business as usual," Murphy said. "It is no time for politics as usual. Therefore, I am today withdrawing as a candidate for governor."

Murphy's aides and advisers said there was no single reason for the decision to withdraw. But they all cited the growing certainty that Murphy could not win and that she could, by splitting the liberal vote, unwittingly help Silber become the Democratic nominee. In addition, her aides said, the Murphy campaign was in debt.

"It's been pretty clear for a long time," Murphy adviser Edward Reilly said. "We were short on money, the mood of the state is very angry." He also said Murphy bore a "heavy burden" as a member of the Dukakis administration at a time when Dukakis is viewed unfavorably by about 80 percent of the state's voters.

In a sense, several observers noted, Murphy was one of the last casualties of Dukakis's 1988 presidential campaign. When the governor returned home in defeat and announced a deficit in the state budget, his popularity plummeted and dragged down all those associated with him.

Murphy, although never a part of Dukakis's inner circle, remained outwardly loyal to the governor until she began edging away from him earlier this year. The final rupture came last week, when Murphy seized on Dukakis's absence to take over state government. In short order, she began issuing executive orders to cut spending, but her actions were largely dismissed as a political stunt.

Both of the remaining Democrats in the race praised Murphy and claimed to find advantage in her withdrawal.

Bellotti has been widening his lead in recent polls and courting Murphy supporters on the grounds that he could win while she could not. Her withdrawal, he said, "helps me because a great many of the people who were with Evelyn Murphy are people who would normally be with me."

Silber, who has come from political obscurity to the second spot in recent polls, said Murphy's decision means "the race starts anew."

"The voters will have a clear choice between the politics of the past, as represented by Frank Bellotti, and the fundamental changes in government that I have proposed," said Silber.