Hewlett-Packard's Portable rides the crest of a hot trend

Computers-to-go is one of the hottest trends in the personal computer (PC) marketplace today. In the past few years, PCs have shrunk from desktop-size to a ''transportable'' or ''luggable'' 20- to 40-pound package. Now they are jumping off the desk and into the briefcase, gaining true portability while retaining the power of their deskbound predecessors.

The prototype of this new class of computer is Hewlett-Packard's 110, prosaically dubbed the Portable. The Portable, announced last May, makes an attractive, compact package. It is the size of a small electronic typewriter (3 inches high, 10 inches deep, and 13 inches wide) and weighs only 9 pounds, yet packs as much computing power as HP's desktop Model 150, or more.

Tailored for the mobile business manager and executive, the Portable does not come cheap. Its price is $2,995, including some software: Lotus Development Corporation's 1-2-3 (an integrated electronic spreadsheet, graphics, and filing package), HP's MemoMaker (a primitive word processor), and a communications package, all of which the company claims would be worth $900 if bought separately. To the total system price, however, one must add $795 for an external disk drive and $495 for a printer.

The Portable was a natural product for Hewlett-Packard to pioneer. As inventor of the hand-held calculator, and the only American company still active in the calculator market, HP has plenty of experience cramming computational power into compact packages and running it on battery power. After a lackluster start, the company has also made a serious commitment to the personal computer market and, according to a number of analysts, has recently moved firmly into third place behind IBM and Apple.

The result is a machine that exudes the quality for which HP has become known. In terms of speed and memory it is the match for most full-size personal computers. It also runs for 16 hours straight on its lead-acid batteries, longer than even the smaller and less capable lap computers like the Radio Shack Model 100.

When you unpack the Portable you discover a solid, white plastic case the size of a large three-ring binder. Two front catches release the flat screen, which swivels up to uncover the keyboard. There is no handle on the case (its innards are too tightly crammed with electronics to fit one, HP says), but it comes with a soft plastic case with a strap.

The most significant difference between the 110 and a desktop computer is its display screen. Instead of a television-like video display terminal (VDT), the 110 sports a silvery, rectangular screen. This liquid crystal display (LCD), like the display used in a digital watch, is the biggest drawback for the 110 and all other portable computers. LCDs are used for two basic reasons: They are flat and compact, and they use little electricity.

In the past, LCDs have also been small, showing less than 20 percent of a standard screen. The Portable, with its 16-line-by-80-column display, does much better in this regard, showing a full two-thirds of the display of a standard VDT. But to achieve this HP was forced to go to smaller characters than those used by previous machines. This, in turn, accentuates another drawback in LCD technology: iffy readability.

The contrast in current LCDs is low and the screen surface is shiny. It is easy to find yourself staring at your own image or that of a window rather than at the characters on the screen. The screen looks best in strong, indirect light. In the proper conditions, it is quite satisfactory. But in less than optimal lighting, readability suffers severely. Early models also had a problem that caused the screen to ripple slightly. HP says this has been corrected. But there have been reports that the company is having problems with the quality of Japanese-supplied LCDs. Prospective buyers would be wise to check the screen quality closely.

The Portable has an impressive amount of software packed into its electronic innards. This resides in what is called read-only memory (ROM) - storage areas the computer can read but cannot alter. HP has also crammed 250 screens of documentation into ROM, so it is generally available at the touch of a key.

In addition, the machine boasts 272,000 characters of working, or random-access, memory (RAM). Although it's larger than many desktop computers, the Portable's RAM must serve two functions. It is divided between active memory (the place where information is stored while it is processed by the computer) and an electronic disk (an area where information is stored for long periods of time). When traveling, this electronic disk takes the place of a diskette, which is normally used for permanent data storage.(Unlike the RAM in most personal computers, which loses all information when the power is turned off, the Portable's RAM retains information as long as its batteries are charged.)

One of the new machine's peculiarities is its lack of a power switch. Simply touch any key and it comes to life. When the screen blinks on, you are most likely to encounter HP's application manager, called PAM. This is a software ''shell'' between the user and the computer's operating system, the popular MSDOS. Operating systems take care of a computer's basic housekeeping functions, but they tend to be cryptic and confusing to new users. PAM makes it easier to do such basic operations as running a program or copying a file.

PAM makes extensive use of the Portable's eight function keys. These are keys that can take on different functions, depending on what the computer is doing. The labels for each key's current effect are listed in a series of small boxes across the bottom of the screen.

The software centerpiece of the Portable package is Lotus's best seller, 1-2- 3. Primarily, this is a powerful electronic spreadsheet for financial planning and calculations. It includes filing and graphing capabilities as well. On the Portable, this popular program is better than ever: It works faster than on most other machines. HP is working with Lotus to upgrade the Portable's 1-2-3 to the newer product, Symphony, which adds word processing and communications capability.

Although Symphony's word processing is not getting as good reviews as some of its competitors, it is bound to be better than HP's MemoMaker, which currently resides in the Portable's ROM. MemoMaker is a rudimentary program, designed specifically for dashing off short notes while on the go. It lacks a number of functions (like search and replace) considered standard on full-fledged word processors.

Communications software is necessary for computers to talk to other computers , particularly for the electronic information services that are becoming increasingly popular. HP's communications program is easy to use and appears to work well with its built-in modem, a device needed to communicate over telephone lines. Some users, however, have reported problems transmitting text files to other computers. So Portable purchasers would be well advised to test their machine's communications capabilities thoroughly during the warranty period.

A review of the Portable would not be complete without mention of its printer and external disk drive. Both are compact and battery-powered.

The printer uses ink-jet technology developed by HP. It forms letters by spitting tiny drops of ink on the paper. It is fast and extremely quiet. Its output is comparable in quality to a good dot matrix printer. The main difference is that its printout becomes lighter as its battery discharges, rather than as a ribbon wears out. Its main limitation is that it can't print on envelopes, since it can't accommodate the thickness of conventional envelopes.

The disk drive uses the new, smaller 3.5-inch diskettes. These are packaged in plastic cases, unlike the standard 5.25 inch diskettes, which are sheathed in cardboard. Those people who already have an HP 150 computer or an IBM PC can probably get by without a disk drive at all. They can buy another useful accessory - the Portable-Desktop Link. This software and hardware package, priced at $150, connects the Portable to the larger computer.