If you're planning a business or vacation air trip, you'd better know your rights when it comes to baggage claims. With many of the airlines running at peak capacity, it's inevitable that some baggage will be lost, damaged or delayed. When something goes wrong with your baggage, that's bad enough. When you don't get compensation for your troubles, that's adding insult to injury.

First off know that the airlines on domestic flights are liable only up to $750 per passenger for lost or damaged luggage. On international flights, they're liable for $9.07 a pound (a 50-pound bag would be worth only $453.50.

If you have expensive clothing or other valuables worth more than the airline's initial liability, you can buy "excess valuation" coverage. You can get the additional coverage at the airline ticket counter for around 10 cents per $100 added value. For example, if you want $600 added value, it would cost 60 cents for each flight, or $1.20 roundtrip, giving you total coverage of $1,350.

You can get baggage insurance also from the insurance counters in most terminals. The charge is based on how long you want the baggage covered. To get $600 extra-coverage baggage insurance for a two-week trip, you'd pay around $13 - a rate higher than the "excess valuation" rate, but the baggage is covered for two weeks in terminals, taxis, hotels lobbies and the like.

The airlines have some loopholes they can use to avoid paying off on lost or damaged baggage. For one thing, the rules say they don't have to pay for such vulnerable items as cash, jewelry, valuable papers and antiques. They suggest you carry these items with you.

Then there's the question of baggage "acceptability" for travel. If the airline feels a bag is too fragile, it won't be checked unless you sign a "waiver of acceptability." Anything the airline accepts without a waiver. it's responsible for. But even if you sign a waiver, the airline still has some responsibility. If the waived item is lost or damaged through provable negligence, the airline is responsible and must offer reimbursement.

If you arrive at your destination all set for a relaxing vacation or a stimulating business meeting and your baggage doesn't arrive, then what?

You might have to rent or purchase special clothing (tennis togs, business suit, tuxedo or evening gown). Or you might have to rent or buy special equipment (tennis racket, golf clubs, hiking gear). If so, you can demand that the airline pay for all out-of-pocket expenses up to the maximum liability. Regarding those purchases, the airlines usually will pay half if you keep the items or 100 percent if you turn over the items to the airline when you're through with them.

Whenever something goes wrong with your baggage, make a claim immediately at the airline counter. Don't wait. The airline could say your bag was lost or damaged elsewhere if you make a delayed claim.

And with expensive, new clothing or equipment be prepared to give proof of purchase (date and value). You must also show your ticket and baggage claim checks. If you're asked to turn over the claim checks, get a receipt and always keep a copy of any claim you make.