Readers constantly share with us their shopping lists for the ideal portable computer: full-size keyboard including calculator style numbers pad; full-size viewing screen, bright and clear; enough RAM memory to run today's new programs; hard disk big enough to store half a dozen programs plus megs of data; batteries big enough to last four hours; a package that weighs five or six pounds.

This is what we tell such dreamers: "If you get what you want, share your secret with us." So far, neither we nor readers have found the dream portable. We have yet to find a portable weighing under 10 pounds that we can recommend.So we continue to stoop whenever we carry around the by-now old Zenith TurbosPort386 "portable." It once had an $8,000 price tag but now sells for $3,000. It meets every requirement on that shopping list but one. Zenith's large screen, decent-size keyboard, big disk and big batteries add up to 18 pounds - without battery charger, manuals, case, data-swapping cord or floppy disks. Those other tote-alongs add 7 lbs.

Totable computers are called many names: portables, laptops, notebooks, etc. There's no standard for when a portable becomes a lap-top or a laptop a notebook, so we call them all portables.

The majority use built-in recharge-able batteries. For battery operation, two comparison factors are vital: how long the batteries operate between chargings and how effective the low battery signal is in getting your attention.

Manufacturers' claims for battery life have nothing to do with real life. Downgrade advertised figures by 50 percent.

Few portables run longer than an hour or two on a charge. Most Zeniths are rated 3 hours, Compaq's LTE models 3.6 hours, the GRID-LITE XL 4. Our Zenith's batteries are rated at 4, but we now get between 2 and 3 hours.

Most portables use nickel-cadmium batteries, and they have a major flaw: charge memory. If you frequently consume only half their power before recharging, they soon store only half as much power. Therefore, you should totally discharge portable computer batteries before recharging.

Rechargers included with most portables take four times longer to charge batteries than it took you to discharge them. Exceptions: Dell's portables take 2 hours to charge and you get 2 hours of use; Compaq's LTE models give 3.6 hours of use and recharge in 1.5 hours with optional charger.

Low battery warnings should give at least one minute advance notice using a signal that can be heard across a modest-size office even when people are talking. If you don't hear the alarm go off, you could lose all of your recent work. There is so much variation, we strongly advise you to test the low-power signal on each particular portable you consider purchasing. Test it again after you buy.

Put keyboard look and feel high up on any requirements list. The actual size of individual keys and overall keyboard is more important than the number of keys. No portable yet has a keyboard well-suited to heavy typing use such as word processing. Most portables' keyboards are awkward. Try them - for a long time - before buying.

Zenith's TurbosPort386 keys are typical of high-end portables: They're about the same size as on a standard desktop keyboard. A 10-digit numbers pad for bookkeeping or calculating is accessed only by holding down a special FN key and punching specially marked double-purpose keys. When the FN key is held down, the top row of keys doubles as IBM-compatible function keys.

A comfortable monitor is as important as a comfortable keyboard. Spend as much time as possible using the screens of portables that make the top of your shopping list. Measure your subjective comfort level on each monitor.

There are three objective variables for evaluating monitors: resolution, display technology and size.

The basic measure of resolution is in graphics standards: CGA and MGA can provide resolution as low as 320x200 dots per screen. EGA is better. VGA can exceed 640x480 and is best for viewing comfort.

Even with careful planning and buying, expect to replace and repair portables more often than desktop computers. Quite simply, they get much more wear and tear. Never haul portables on wheeled luggage totes because bumps bring quick death.