Nurses at one of Harvard's major teaching hospitals voted overwhelmingly Monday night to strike if the hospital does not meet demands for greater job security and improved benefits.

More than 84 percent of the 1,400 registered nurses at Brigham and Women's Hospital in Boston voted to strike as early as Oct. 1, after more than one year of contract negotiations with the Massachusetts Nurses Association failed to reach agreement.

Some nurses began picketing outside the hospital yesterday.

A strike could devastate the hospital, ranked the eighth-best in America last month by U.S. News and World Report, and hurt Partners HealthCare Systems Inc., the $1.8 billion conglomerate formed by the 1993 merger of Brigham and Women's Hospital and Massachusetts General Hospital, another University teaching hospital.

Registered nurses reportedly said they were concerned the hospital would lessen the quality of patient care by cutting the nurse-patient ratio, thus requiring unlicensed aides to perform more duties.

Nurses also said they were concerned about proposals to change health care coverage and the seniority system, which provides higher pay for more experienced nurses, and the hospital's assertion that is has the right to transfer unionized nurses to other non-union hospitals in the Partners HealthCare network, such as Mass. General.

However, Brigham and Women's vice president of nursing, Mary Fay, said there are no plans to get rid of registered nurses or to take away their right to determine which tasks unlicensed assistants can perform.

The current contract expires Sept. 30, but for registered nurses to walk out they must give 10 days' notice by tomorrow.

Negotiations are continuing, with three sessions scheduled before the contract expires.

--Wire dispatches contributed to this report.