Following the 14-hour flight from Bangkok to Seattle, you stand, exhausted, before the Customs inspector. Your ears are so stuffed you hardly hear him say, "Open that bag, please."

As you do so, carry-on items erupt onto the counter. Among these is a papaya you'd forgotten to eat during the journey.Travelers delayed behind you glare suspiciously as the inspector interrogates you and eventually confiscates the fruit. In failing to declare it, you broke the law.

It's that easy to become a "criminal" while going through Customs. Even forgotten fruit - prohibited because crop-killing parasites may be present - gives you a "record."

Embarrassment and confiscation are minor compared to jail terms or fines imposed for illegal drugs, firearms or counterfeit goods, but computerized files give inspectors instant information about past infractions which, however slight, can cause annoying delays following future excursions abroad.

Your best defense: know and abide by regulations. All purchases and gifts acquired abroad, plus repairs and alterations, must be declared.

Provided you've been abroad at least 48 hours and haven't used your exemption within the previous 30 days, your exemption is $400, (or $600 from Caribbean basin countries) including one liter of alcoholic beverage (prohibited by some states) and 200 cigarettes or 100 cigars (Cuban cigars only if purchased in Cuba).

Keep receipts handy to show value, especially on high ticket items. Families may combine exemptions, but minors may not import alcoholic beverages or tobacco.

If you don't meet the 48-hour or 30-day requirements, your exemption is $25, including 50 cigarettes or 10 cigars, plus 4 fluid ounces of alcoholic beverage or perfume, and may not be declared on a family basis.

Travelers returning from the U.S. Virgin Islands, Samoa or Guam have $1,200 in exemptions, including five liters of alcoholic beverage.

If acquisitions exceed exemptions, 10 percent is charged on the next $1,000 worth of merchandise (or 5 percent if you're returning from the U.S. Virgin Islands, Samoa and Guam). Thereafter, individual articles are variously dutiable, and rates may be obtained from U.S. Customs Offices.

You must have valid prescriptions for any drugs or drug paraphernalia you're carrying; firearms and ammunition require special permits.

Additional restrictions apply to foodstuffs: uncured cheeses, fresh or prepared meats, poultry and fish not hermetically sealed, fresh vegetables and fruit. Rooted plants, seeds or cuttings are not allowed.

Products made from endangered species - the lengthy list covers tortoises, spotted cats, rare birds, elephants, whales, most monkeys, alligators and crocodiles, many snakes and lizards - are prohibited, as are ceramic tableware with lead-based glazes, automobiles that don't meet EPA standards and pre-Columbian or other artifacts unless you've got permits from countries of origin.

Surprisingly, the law allows travelers to import - in limited quantity and for personal use only - copies of many trademarked articles, including famous-maker watches, perfumes, clothing, leather items, cameras and electronic goods. Larger quantities of these counterfeits are confiscated and importers fined or imprisoned.

Although not restricted, currency, checks or securities over $10,000 must be reported on Customs Form 4790.

When crossing borders, don't try to joke with Customs agents. And whenever in doubt, declare!

Contact the U.S. Customs Service, Department of the Treasury, Washington, D.C., 20229 for more information or, before buying merchandise abroad, call the nearest American embassy for advice.