The woman, identified as Jennifer San Marco, 44, of Grant, N.M., a former employee of the Santa Barbara Processing and Distribution Center, confronted employees with a 9 mm handgun, the authorities said.

The 80 or so employees in the building fled as she fired, said Sheriff Jim Anderson, of Santa Barbara County.

The authorities had not determined if she was selecting the victims, all women except one, or shooting at random in what was one of the deadliest rampages at a Postal Service building.

After working as a sorting clerk for six years, the woman went on medical disability for unspecified mental problems in June 2003 after co-workers reported her acting strangely and called sheriff's deputies, postal authorities said.

''She wasn't considered a threat to anybody, but she was acting in a way that concerned employees,'' Randy DeGasperin, a U.S. Postal inspector, said of the 2003 incident. ''They called deputies more for the safety of herself.''

Monday's workplace shooting was thought to be the deadliest carried out by a woman and the highest toll since a worker at an aircraft parts plant in Meridian, Miss., killed six colleagues and wounded eight others in 2003.

The violence provided a flashback to the spate of shootings at post offices and related facilities in the 1980s and '90s.

The last such shooting was eight years ago in Dallas, when a letter carrier killed a clerk after arguing in a break room. The deadliest was the August 1986 killings of 14 people by a co-worker in Edmond, Okla., who then killed himself.

''Going postal'' entered the lexicon, but an independent report, based on a two-year study and prepared for the postmaster-general in 2000, said postal workers were no more inclined than others to commit workplace violence.

What was unusual about this workplace shooting was that a woman committed it.

From 1976 to 2004, women made up just under 5 percent of the people who committed mass shootings and about 7 percent of those who killed in the workplace, said James Alan Fox, a criminologist at Northeastern University in Boston who has studied workplace crime.