A just-published, three-volume directory of almost 70,000 businesses in the Washington area fills the needs of those who demand a quick, complete reference library to the region's commerce.

Compiled and distributed by Engleman-Potomac Inc. of Alexandria, a franchise operation of Contacts Influential Ltd. of Portland, Ore., the directory organizes information on area businesses in several useful ways.

First, an alphabetical list gives the name of the company, what it does, its address, how old it is, how many employes it has and the names and titles of its top executives. Companies are then listed generically using standard investors classification (SIC) numbers. A third section, market planning, lists the number of firms under different categories -- the number of firms in a certain zip code, the number of bakeries or banks. Another section organizes companies according to their zip code and street address.

There also is an alphabetical index of all the top business people and a list of telephone numbers.

Published recently are one directory each for the District, Northern Virginia and Montgomery and Prince George's counties.

"We're concentrating on both big and small businesses," said Eli Argon, marketing representative for Engleman Potomac, which services the East Coast. "There is no financial discrimination."

So far only 300 copies of each volume have been printed. They are leased on an annual basis and updated monthly with any additions or corrections. The Maryland and District directories cost $480 a year each and the Northern Virginia book is $365.

Argon points out that the directory is particularly valuable to any firm is planning expansion into a certain market by giving it information on where certain businesses are concentrated. In the past month, Argon has leased directories to stockbrokers, personnel agencies, real estate firms, hotels and insurance companies.

Contacts Influential was started 15 years ago and now has directories for 21 cities, including Atlanta, San Francisco and Dallas.

Work on the Washington area directories was begun last November with calls and letters to a variety of sources. The company purchased information anywhere it could and also walked through the Bell System "yellow pages" and corporate registration statements.

After the data was compiled, each company was contacted by telephone to verify the information, which was then fed into a computer. The company guarantees 95 percent accuracy.