MALL PATROL : WHEN TOO CASUAL ISN'T COOL.

Byline: Barbara De Witt 

It's hot outside, the office air conditioner is down, and short-shorts are looking mighty good for casual Friday.

Resist it.

Laura Stephans, Mervyn's California fashion consultant, suggests khakis, long cotton skirts, cotton sweater sets and denim jumpers over T-shirts instead.

``The trick to business casual during the warmer months is creating a comfortable look while maintaining professionalism and authority,'' Stephans said.

Mervyn's has a new line of clothes called Office Supplies, aimed at cool and collected professionals. Maybe you're well-dressed, but think your office colleagues need help?

Stephans gives free seminars and handbooks to local businesses who are interested in providing information on the subject, and she has a new video on the subject for $30. For more information, call [phone], Ext. 233.

Women have so much help these days, from booster bras to magic panel pantyhose. Now the guys have a girdle ... of sorts. Scheduled to arrive in local department stores including Macy's and Bloomingdale's by July 25 is Claiborne's Spa shirt. A cotton dress shirt, it's cut and designed to make a man look a little trimmer and to fool people into thinking he's been working out. The Spa shirt costs $45 and comes in white, blue or stripes.

But back to women's lingerie. At Robinsons-May stores you can find push-up bras by Olga designed just for petites in sizes AA, A and B, priced at $24. While you're there, try on Olga's new Secret Shapers collection of slips with a built-in girdle for $29. It's cool for those skimpy little tank dresses because the slip is A-lined to swing with the skirt, while the panty girdle smooths thunder thighs.

Still haven't stocked up on sandals? If you're wondering what local celebs are favoring for their feet, take note. Actress Angie Everhart, from ``Jade'' and the coming summer flick ``Tales From the Crypt,'' picked up a bunch of clunky-heeled sandals by Miu Miu at the trendy Madison boutique, 106 S. Robertson Blvd., Los Angeles.

For style on the cheap, however, Old Navy stores now carry shoes priced from $2.50 to $26 a pair. Especially cool are the orange mules and lime thongs.

By now you know Todd Oldham has opened a boutique at 7386 Beverly Blvd., Los Angeles. The young designer who's best known for bringing back '70s polyester fashions and bright colors has created a high-energy store that's low on stuffiness. It's a friendly atmosphere with chatty saleswomen, reasonable prices, and cute but overpriced costume jewelry, like stackable gold-toned rings set with colorful crystals. The metal crown pendants for about $10 and up are the best deal.

Where designer clothes, hand-painted ties, makeup come together Today: Venice Art Walk begins at 11 a.m. at Westminster School, 1010 Abbott Kinney Blvd., Venice. You'll find hand-painted ties, handcrafted jewelry and clothing, besides food, theatrical performances and auctions. Admission is $45 per person and benefits the Venice Family Clinic. For more information, call [phone], Ext. 333.

Tuesday: Makeup artist Trish McEvoy will make a personal appearance from 10 a.m. to 2 p.m. at Nordstrom at the Glendale Galleria, 200 W. Broadway, Glendale; and from 3 to 8 p.m. at Nordstrom, Topanga Plaza, 6602 Topanga Canyon Blvd., Canoga Park.

Wednesday: Makeup artist Trish McEvoy will share makeup tips and present her new cosmetic line at Nordstrom, Westside Pavilion, 10830 W. Pico Blvd., Los Angles. Hours are 12:30 p.m. to 5 p.m.

Wednesday, Thursday: Karl Lagerfeld fashions will be modeled informally between noon and 3 p.m. in the couture salon of Neiman Marcus, 9700 Wilshire Blvd., Beverly Hills.

Thursday: Woodbury University's 32nd annual fashion show will be held at 8 p.m. at the Biltmore Hotel in Los Angeles. Admission is $25. For more information: [phone], Ext. 332.

Thursday: Elite Modeling Agency and Guess?? jeans will sponsor a model search at 4:30 p.m. at the Promenade Mall in Woodland Hills. This is an ``open call'' for young women, with no registration fee. A fashion show follows at 7 p.m.

Friday: The American College of Los Angeles will hold its annual student fashion show at 7 p.m. in the Beverly Hilton Hotel, 9876 Wilshire Blvd., Beverly Hills. For more information call [phone].

May 26: ``Colors of the Wind,'' an entertainment and family fashion show by Enhance Productions, at 5 p.m. at Best Western Mission Hills Inn, 10621 Sepulveda Blvd., Mission Hills. Admission is $10. For more information call [phone].

May 30: Trunk show of Marie St. John's fall fashions will be held from noon to 3 p.m. with informal modeling at Macy's, 401 S. Lake Ave., Pasadena.

May 30-31: Pamela Dennis' fall fashions will be previewed with informal modeling from noon to 3 p.m. in the couture salon of Neiman Marcus, 9700 Wilshire Blvd., Beverly Hills.

June 1: The Fashion Industries Guild of Cedars-Sinai Medical Center will hold its third annual Manufacturers' Charity Sale to benefit children born with HIV. The event will be held from 9 a.m. to 5 p.m. at the CaliforniaMart, 110 E. Ninth St., Los Angeles. It's a cash-only sale of new merchandise from Carole Little, Rampage, Platinum, a.b.s., Laundry, Karen Kane, Guess? and other leading brand names for men, women and children. Admission is $1.

June 8: You'll find western shirts and jackets, rodeo apparel and military flight uniforms at the Flying Deuce Vintage Denim Auction and Sale, which begins at 1:30 p.m. at the Pasadena Center, 300 E. Green St., Pasadena. Admission is $10. For more information, call [phone].

June 8-9: The Best of Macy's fashion show featuring clothes for men and women will be held at 1:30 p.m. in the main court of the Glendale Galleria, 200 W. Broadway, Glendale.

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Photo: (1--3) Professional correct clothes for casual Fr idays include Ellemenno loafers, $24; silver-tipped belts, $18; drawstring pants, $29; and khaki jacket, $54; all from Mervyn's new Office Supplies collection.