Santa does not do e-mail. Nor does he respond to text messages. If you want to contact Santa, you have to write a letter, an ancient practice involving paper, pencil and a stamp.

Thousands of Bay Area children have done just that - but this holiday season, the tone of letters bound for the North Pole is a little more somber than usual. U.S. Postal Service officials in Oakland and San Francisco said they've seen a sharp increase this year in kids asking Santa not for Xboxes or PlayStations, but food, warm coats and jobs for their parents.

"It really tugs at your heartstrings," said Augustine Ruiz, a Postal Service spokesman. "We try to answer every one, so they know someone cares."

This year, post offices in the greater Bay Area have received more than 6,100 letters addressed to Santa, a high percentage of them asking for the bare essentials (plus maybe a Barbie Dreamhouse).

Isaac in San Jose asked for juice, a new pen and "a picture of Grandpa and me." Jacqueline in Oakland, with immaculate handwriting, asked for an iPad so she can do her homework, explaining that her parents can't afford a computer and in fact Santa did not come at all last year. She promised to share it with her sister. A girl in Vallejo asked for a place to live.

"The little boy or girl who recognizes that Mom or Dad doesn't have a job... the first week we do this, all my tears are gone. I have no more tears to cry," said Marygrace Cruz, consumer and industry manager for the Postal Service's Oakland district. "This is the most rewarding thing we do all year."

Santa's elves, a.k.a. postal employees, carefully separate the letters into those from children who appear impoverished and those who just have a strong interest in Santa. The latter group receives letters from Santa in return, thanking them for believing and wishing them a happy holiday.

The former group gets special treatment. The Postal Service deletes the children's last names and addresses, and puts the letters in the main post office lobby for the public to peruse. Volunteers can pick a few letters, buy whatever the child is requesting - or gift cards, money orders or anything else that seems appropriate - wrap it up and give it to the Postal Service to send to the child.

To protect the children's identities, the Postal Service - not the volunteer - mails the packages.

Volunteers pitch in

Sometimes companies or schools take stacks of letters. A high school in Danville took hundreds. A tech company in Alameda took dozens, giving all the kids computers. A few volunteers bought bikes for kids, which Cruz hand-delivered.

Diane Banks of San Pablo and Tami Williams of Dublin, co-workers at the Oakland Housing Authority, were at the city's main post office on a recent afternoon and could not tear themselves away from the Santa boxes.

"I think this is absolutely wonderful. Heartbreaking and wonderful," Williams said as she sorted through the letters. "Even though the economy is not great, it's important to put a smile on a kid's face at Christmastime. I certainly get that."

She stopped at a letter scrawled in crayon, with drawings of Christmas trees.

"This kid wants an MP3 player with black headphones. Bless his sweet heart," Williams said. "You got it, buddy."

Emotional response

Banks wept as she flipped through letters.

"I was just expecting kids wanting toys and stuff," she said. "I didn't know they'd tell so much about their situations. This is just very moving."

One letter said, "My name is Brian and I have three brothers. Fernando is 7 years old and Edwin is 12 and the baby is 1. I have only my mom my dad isn't here. I would like a bike. ... I love you Santa."

Another girl said there was a fire at her house. A woman in Vallejo asked Santa for a full-time job so she could buy gifts for her kids next Christmas.

Even the police officer guarding the lobby was sucked in. He said he grabs a few every year, looking for kids who live in his hometown of San Pablo.

"I don't have kids, so this gives me a chance to give some toys," said Terry Hinton. "It's a good thing, I like it. Puts me in the Christmas spirit."

There's still time Volunteer elves can stop by the Oakland main post office through 3 p.m. Thursday to respond to a child's letter from Santa. The address is 1675 Seventh St. For more information, go to http://1.usa.gov/1hhhiAd

Carolyn Jones is a San Francisco Chronicle staff writer. E-mail: carolynjones@sfchronicle.com