The San Francisco Sheriff’s Department is conducting a sweeping internal investigation into allegations that several deputies severely beat inmates and conducted degrading strip searches.

Sheriff Vicki Hennessy said Wednesday that the investigation began Dec. 2 after an employee and the public defender’s office brought the alleged abuses to her attention.

“We’re taking this extremely seriously, but we have a lot of work to do,” she said. “One of the last things we do is interview deputy sheriffs involved.”

According to a report provided by Public Defender Jeff Adachi’s office, 15 men said they were assaulted or abused at the San Bruno jail, and 16 women said they were inappropriately strip-searched.

Among the allegations:

• One man said deputies knocked him to the ground and took turns kicking him.

• Another said he was dragged in handcuffs.

• Another man said he was beaten three times on the same day in September, and then taken to the hospital because he was bleeding from his ear.

• Some of the women said the strip searches were conducted in full view of male deputies.

• One said she was strip-searched twice in two days, and after the second occasion deputies took her clothes and transported her back to her cell naked.

Adachi filed a formal complaint with the Sheriff’s Department last month, describing the jails’ conditions as “deplorable,” and the deputies’ treatment as “ongoing and repeated misconduct,” according to a copy of his Jan. 16 letter to Hennessy.

Adachi wrote that his office’s “clients are fearful of retaliation for coming forward with their complaints. Despite their fear, some are prepared to come forward with their complaints if necessary.”

In a Jan. 31 response to Adachi, Hennessy disagreed with his description of the jails as “deplorable” but thanked him for his assistance in bringing details to her attention. Hennessy added that she is “reviewing our inmate living area search policies to ensure best practices.”

Hennessy’s five-person investigation team is reviewing “hours and hours” of video footage from the jails, and is prioritizing the more serious allegations, she said. “Less than a dozen” employees are under investigation, she added.

“I have to keep an open mind,” she told The Chronicle. “I don’t want to prejudge things — both for the inmates and for the deputies involved.”

Adachi told The Chronicle that the nature and volume of the accusations should warrant an independent investigation or oversight.

Hennessy said she hasn’t ruled out the option of an independent investigator.

San Francisco Supervisor Shamann Walton, meanwhile, has called for a hearing on the matter, which is tentatively scheduled for March 14 at the board’s public safety and neighborhood services committee meeting. The supervisors are asking the Sheriff’s Department for statistics on inmate complaints, for information on who investigates inmate complaints, and any actions taken.

“Being in jail is a very vulnerable place to be,” Adachi said. “If you’re attacked by a sheriff’s deputy are you going to call the cops? We want to make sure that there’s a process in place such that any complaints are investigated.”

San Francisco Deputy Sheriffs’ Association President Ken Lomba said the union welcomes the investigation and “full transparency,” but questioned Adachi’s motives.

“This is eerily similar to Jeff Adachi’s war on the democratic judges,” he said in an emailed statement. “Now he is attacking the Sheriff’s Department as a possible means to fund-raise for the district attorney’s race.”

Megan Cassidy is a San Francisco Chronicle staff writer. Email: megan.cassidy@sfchronicle.com Twitter: @meganrcassidy