Microsoft Corp. is probably the single most important source of software for personal computers, and word processing is probably the single most important software application for personal computers. You might expect, consequently, that Microsoft would offer a first-rate word processing program.

I drew that seemingly sensible conclusion and invested in Microsoft Word when it became available last year. I was disappointed. I found the first version of Word to be slow, complicated, and lacking in features expected from a $300 package.

The maddening thing about Word is that it has enormous power -- but a lot of the power is consumed by features most home and business users hardly need. Do you really need to set margins and indentations precise to the hundredth of an inch? Word not only permits this, but requires it. And yet that first version of Word did not provide such essentials as a spelling checker or a word counter.

Microsoft has just released version 2.0 of Word, which I've been test-driving for a couple of months. (I'm using the IBM-PC varient, which is similar to, but more powerful than, the version for Macintosh). I've found Version 2 a big improvement, but still disappointing.

In its new version, Word still centers on a set of extremely detailed, and thus complicated, formating commands. If you have one of the new ink-jet or laser printers, you can design your final document to a fare-thee- well. Otherwise, that formating power could be excess baggage.

Word now comes with a separate disk containing utilities such as a spelling checker. Microsoft advertises that these are "built in." They aren't. To use the spelling checker or word counter, you have to stop writing, save your document on a disk, call up a separate program, insert a new program disk, and reload your document -- only then can you run the speller. Other programs, in contrast, check spelling or count the number of words with one or two quick keystrokes.

I'd be happier if Microsoft really had "built in" the spelling checker and other common functions and relegated the heavy-duty formating commands to the separate disk.

In its Multiplan spreadsheet, Microsoft came up with an ingenious command structure: It included menus for uncertain users but let the more experienced glide past the tedious menu structure with one-letter commands. Word uses the same system, so giving commands becomes a breeze. But using Word, particularly for formating and printing a document, can be exasperating, because there are layers upon layers of commands. It seems so easy, for example, to set a tab stop in Word. You can work step-by-step through the menu, or you can invoke the simple, quick commands: F, T, S (standing for "Format", "Tab," "Set"). But then you have to measure the tab to the tenth of an inch and decide what kind of tab it should be (there are four options) and other requirements. I gave up before I had succeeded in setting a single tab stop.

If you're able to get around these problems and master the program, Word has some wonderful features. It lets you leave your document temporarily to run DOS commands or use your modem program -- and then come instantly back to Word where you left it. (This seems to require at least 320K of memory.) It automatically gets maximum use from your printer: If your printer can't print italics, Word sends a command to underline the sentence instead, something most printers can do.

Word does windows -- you can split the IBM screen into as many as eight separate segments (how anybody could use eight windows at once is a mystery to me). I've found this to be a terrific feature -- but here, too, Microsoft fouled up. Whenever you split the screen to make a window, your original document shows up -- again -- in the new window. To put a separate document -- an outline, say, or research notes -- in the new window, you first must go through the slow process of clearing out your original document. Why the program was designed this way is a mystery to me, but it makes the windowing feature much less convenient.

In short, Version 2 of Word can be a terrific program for somebody with a high-powered printer and the need to design picture-perfect letters and documents. For the ordinary user, though, it might make sense to wait for Version 3.

And yet there is one terrific innovation that makes it simple to decide if the new Word is for you. Microsoft is offering a 30-day, money-back offer. If you decide after the first month, as I have, that Microsoft put the power in the wrong places, you can take the program back. This is a wise and commendable marketing course for the software industry, and I commend Microsoft for blazing the trail.