The Catch of the Month : Dating: A picture is worth 1,000 words. For Cosmo’s bachelors, it’s worth 1,000 letters from interested women.

Dr. Fred Kogen expects so much mail that he’s planning a party to open letters all night long.

“We’ll make one pile of good prospects and one pile to read out loud for laughs,” says the Santa Monica internist, who’s been pronounced a good catch by Cosmopolitan magazine.

Kogen, 32, is single, “very available,” six feet tall, 160 pounds. He has blue eyes, brown hair and a good ol’ boy nature that made him say “yes” when his medical assistant asked a few months back if she could send his photo to the magazine.

Now he’s the April Bachelor of the Month, which means he’s a one-paragraph blurb and photo at the bottom corner of Page 168.

This small mention, says Cosmo chief Helen Gurley Brown, practically assures he’ll get up to 1,000 letters from love-hungry women around the globe.

It’s a bachelor’s fantasy come true, says Jerry Brown, who ought to know.

The Los Angeles firefighter was March’s featured bachelor, and he never dreamed there were so many women out there who’d go gaga over a guy like him.

“They give their names, addresses, phone numbers, weight and full measurements,” says the 34-year-old Brown, who lives in Long Beach. “They send photos, audio- and videocassettes. There’s nothing too personal to write about, it seems.”

Most letters are sweet, honest and simple, he says, and accompanied by photos of young women he’d be pleased to meet. Others are--well--strange.

“I used to be a nun until the urges came,” reads one. “Now I’m a dynamo, waiting for you.”

Another starts: “I’m not looking for a relationship, which is precisely why I’m writing. So if you think I’m a potential (girlfriend), forget it!”

A few are really sad. Like the one written in tiny script on both sides of seven pages. The writer explains that the man she was dating dropped her, she accidentally crashed her car into a tree, spent a month and a half in the hospital and now is left with $90,000 in bills. “I was an emotional wreck while I read it,” Brown recalls.

But mostly, he’s overjoyed with his new celebrity and social resources: “It’s awesome. Unbelievable. I haven’t had this much fun in years.”

Trouble is, he works 24-hour shifts at Firehouse No. 5, sometimes two or three days in a row. And few of those who wrote live in cities nearby. He’s met one or two and says they’re “really great. But can you imagine if I had time, if I could go all over the world meeting these girls? I’m sure there’d be someone for me.”

Kogen hopes to make the time. He’s big on travel anyway, he says, but he can’t imagine there will be many women he’ll want to meet. He’s a mountain climber, scuba diver and--in his spare time--performs ceremonial circumcisions on babies of the Reform Jewish faith.

It probably will be hard to find women whose interests match his, Kogen says, but life is too short not to try.

Cosmopolitan founder Brown says the feature has been running about 14 or 15 years: “We check to see that the bachelors are single and don’t have a criminal record.”

Beyond that, everyone must proceed at his or her own risk.