Amid the excitement over the increasingly powerful laptop computers coming to market labeled "notebook" systems, the original notebook computer, the Radio Shack Model 100 (since replaced by the Tandy 102), has all but dropped out of sight. For many, though, it may still be the best buy of all.

The Tandy 102 weighs three pounds, runs as long as 20 hours on four AA batteries, and has built-in software for word processing, telecommunications and keeping an address book and schedule. These programs are about as simple to use as software can be and are the last programs that Bill Gates, the brilliant boss of Microsoft, wrote himself before he became the most powerful man in the industry.

For the record, the 102 comes with 32K of memory, a 300-baud internal modem, a parallel and serial port and an eight-line, 40-column liquid crystal screen that is not back-lit but is easy to read in almost any light. An eight-line screen takes some getting used to, but it can be done. The keyboard is one of the system's best features, with full-size letter and number keys. The function and arrow keys are narrow, in a row across the top.

The 102 retails for $599, but Radio Shack regularly puts it on sale for $100 less. Or you can buy a used one from Shreve Systems, in Shreveport, La., (318) 635-1121, for $325.

You're probably wondering how such a computer, with so little memory, can measure up to the 640K, disk-drive equipped IBM-compatible models that now dominate the laptop market. But with a little enhancement, the model 102 can hold its own against these heavier and more expensive models -- at least for the writing, transmitting and schedule-keeping that are the staples of so much computing on the road.

The first thing you need is some extra memory. There are several options, among them a cigarette-pack size unit from a California company called American Cryptronics, (714) 540-1174, that adds 128K for $199. This almost weightless little box attaches to the computer's bus connector in the rear. It comes with a ROM chip that pops into a slot designed for such things on the computer's underside.

The ROM chip contains operating software for the memory, which is divided into four banks of 32K each, giving you, in effect, five 102's in one. You can copy files from bank to bank, delete or rename them, and set the system time and date. And you can set the computer to automatically send a carriage return and line feed at the end of every line when printing.

This last option is useful. Most printers do not do this automatically, so when you use a printer not set specifically for a Tandy computer, your file will print all on one line. Being able to add a carriage return and line feed lets your 102 share a printer with your office IBM-compatible without your having to reset switches in the printer.

The next thing you need is to improve Text, the built-in word processing software. The best way is with a program called Supera, $79.95 from Ultrasoft Innovations of Champlain, N.Y., (514) 487-9293. This is a macro program that comes with a number of useful writing macros built in. The macros provide single-keystroke commands for deleting a word to the left or right of the cursor, deleting to the end or start of a line, or to the end or start of a file.

Supera also adds full search-and-replace capability and includes a keystroke to change the case of a letter -- very handy -- and to turn the computer off so that when you turn it back on, you go right back to where you were. You can, of course, write your own macros with this program, which despite its tiny size (less than 4K) rivals such IBM-compatible programs as Prokey and Superkey for power and versatility. The 102's telecommunications software, Telcom, works well with the 300-baud modem, but if you attach a faster portable modem to the serial port, a number of Telcom features won't work, including auto-dial and auto-logon. Fortunately, there is public-domain software to solve this. You can get it, among other places, from Club 100, a model 100102 support organization in California, (415) 932-8856.

Richard Hanson, who runs Club 100, sells a variety of other 100102 enhancements, including programs to exchange files through a serial connection with your desktop computer. There's also a $199 ROM-based collection called Super ROM from Portable Computer Support Group of Dallas, (214) 404-3030, with a spreadsheet and database.

Brit Hume is a contributor to the Washington Post Writers Group. He is chief ABC News White House correspondent and the founding editor of a computer newsletter.