David Horowitz believes that if someone is trying to rip you off for even a dime, you should fight back. He does. Almost daily, it seems.

In a Washington company cafeteria last week he ordered ice tea. A clerk handed him a paper cup filled to the top with crushed ice and directed him to a tea dispenser. Instead, he asked for a second empty cup. This he filled with the tea.

"You notice how they always fill the cup with ice," he said to the two men who accompanied him and who had done exactly what the cafeteria clerk had instructed them to do. "You get a lot of ice and a little drink." With his separate cup of ice and tea, he noted, he got twice as much to drink as his two companions at the same price.

The day before, he says, he told a waiter in a Boston hotel there would be not tip because the eggs he's ordered "over easy" came hard. He relented only when the waiter brought back a second order within five minutes.

At a posh San Francisco hotel, he sent the eggs back four times because they were hard. "I got a lot of flack, but I told them, 'If you've got a chef who doesn't know how to poach eggs, you ought to get another.'

"Nothing is worse than getting angry and doing nothing about it," writes Horowitz, 42, a consumer reporter for the National Broadcasting Company, in his first book, "Fight Back! and Don't Get Ripped Off" (Harper & Row, $8;95, 308 pages). His syndicated show, "Consumer Buyline," is shown locally Sundays at 1 p;m. on ABC, and he is a frequent guest on the talk-show circuit.

His book, he readily acknowledges, is something of a half-time pep talk for a consumer buffeted on all sides by "the hype, the salesperson's spiel, the seductive advertisement, or the blatant mispresentation." To make his point clear, he tells you in big bold letters at the end of each chapter, "FIGHT BACK!"

People are being shortchanged in one way or another all the time because they're not "savvy" to what is going on. He wants to make them aware and send them out in the world better able to protect themselves. When they win a battle, he argues, they're not only saving their own money in the face of high inflation, they're helping their fellow consumers.

Fighting back takes time, he says -- time to write letters, make phone calls, do your research -- but it's time well spent.

Fighting back also takes guts. You may even have to make a scene.

Recently Horowitz was dining in a restaurant with friends, one of whom ordered Lake Superior whitefish. "Is this fresh or frozen," Horowitz wanted to know and followed the restaurant owner into the kitchen to be shown the box the fish was shipped in and the invoice that accompanied it. "The people I was with were totally shocked," he says.

Another time he took his wife out to "a fairly expensive" Los Angeles restaurant for their anniversary. The service was lousy; There was no water on the table, and he had to ask the waiter for a knife and a napkin. He asked three times before the coffee finally came. He told the waiter, "I'm not leaving a tip. You've hurt my evening. I've been hassled. I've had to tell you your job."

Some of Horowitz's other reminders:

If a bargain seems too good to be true, it usually is.

If you do get ripped off, there's a whole army of government agencies and action-minded organizations waiting to help you get satisfaction.

Have facts at your fingertips -- sales slips, warranties. Send only copies with a complaint letter; keep the original;

When you're buying an appliance, read the warranty and the instruction manual; If you don't understand, ask.

Don't allow yourself to be "intimidated, embarrassed or conned" by putting such professionals as doctors, lawyers and dentists on a pedestal. "An increasing number of the people we trust and turn to have sold out for cash," he writes.