Now, a microcomputer you can tote that has plenty of power

Luggable microcomputers are powerful but weigh a hefty 20 to 25 pounds. Notebook-size computers are small enough to fit comfortably on your lap, but they aren't very powerful.

Now the computer industry may have the real thing: a computer that's small and powerful.

Hewlett-Packard (HP) unveiled such a machine recently. Prosaically called ''the Portable,'' it retails for $2,995 and comes with built-in software and the largest flat display screen made so far. Because of its chip technology, it can run for a week without a recharge.

True portability, proponents say, will make a major change in where and how computers are used. It will provide business people who spend a good part of their lives on the road with all the benefits of a full-fledged computer. Precursors to these ''true portables'' have tended to be either extremely expensive or substantially limited in capability. The Radio Shack's Model 100 ($ 800-$1,200) with its relatively large display and built-in telephone communications was an instant success when introduced a year ago. Its popularity , despite modest capability, suggests strong demand for portability.

Dataquest International, a computer research firm, estimates sales of portables will grow from last year's 500,000 units to 5.6 million in 1988 - about half the projected size of the desktop market. HP has a head start in this market and a $10 million marketing budget to rely on. Competitors - including IBM, Kaypro, and a major Japanese company - are expected to unveil powerful portables this year.

Norman R. DeWitt, an industry analyst at Dataquest, calls the Portable ''an exciting, impressive new machine.'' It has more speed and power than most desktop computers, yet is the size and shape of a small electronic typewriter and weighs only nine pounds. Mr. DeWitt expects HP to sell all of the 70,000 portables it can produce in the coming year. He also believes its popularity will perk up the sluggish sales of the desktop 150 model.

The new portable comes with a comfortable, full-size keyboard. With 16 lines and 80 columns, the silvery liquid crystal display screen (like those on digital watches) can be hard to read in poor lighting but is extremely compact and draws little power. The Portable's central microprocessor is the Intel 8086, a close but more powerful cousin to that of the IBM Personal Computer.

''Our goal was to create a fully portable computer without any compromise in power or functionality,'' says Daniel Terpack of HP's Portable Computer Division.

To achieve this, the HP machine uses state-of-the-art CMOS chip technology. This energy-stingy chip can operate about a week between battery charges. Like continuous-memory calculators, but not most computers, CMOS circuits do not lose information when the power is off. The Portable has enough memory to store more than 200 typewritten pages of text.

In addition, a version of the nation's best-selling business software program , Lotus 1-2-3, is built into the computer's permanent memory. The machine also comes equipped with a simple word processing program and a communications package using a built-in modem, for telephone connections. Owners of the IBM Personal Computer or a fully compatible version may want a $125 circuit board which will let them transfer information rapidly between the two computers.

Although the HP portable and the IBM PC share the same operating system, the program that takes care of basic computer housekeeping chores, only a limited number of programs written for the PC will run on the portable without modification. Dataquest's DeWitt considers this one of the machine's few shortcomings.