CongressStack was born last summer during a long car ride back to Washington from Apple Computer Inc.'s MacWorld trade show in Boston.

Inspired by Apple's "Hypercard" programming software, Dave Drake and Anne-Marie Barker, the two principals of Falls Church-based Highlighted Data Inc., came up with what they see as the ultimate inside-the-Beltway lobbying tool: a computer program that puts all 540 members of Congress, 300 congressional committees and thousands of Capitol Hill staffers within a few clicks of each other on a computer keyboard. Biographies, district maps and zip codes, pictures of every member, 12,000 addresses and phone numbers -- they're all on CongressStack.

"This is a natural for anyone who has to do business with government," Barker said. "Everyone we've shown it to so far has bought it."

CongressStack is the first major product of Drake and Barker, whose small two-year-old firm specializes in adapting large data bases to personal computers. Highlighted is also about to introduce a computerized version of Webster's dictionary, and an electronic map cabinet that offers computerized access to every road map in the country.

But only CongressStack uses Hypercard, the Macintosh software that allows for effortless organization and access to large amounts of information. Imagine, for example, a room full of filing cabinets. Hypercard allows the computer user to browse through the cabinets electronically, selecting and viewing files from each cabinet in multiple combinations, rearranging, adding, subtracting, reading at will.

By putting CongressStack on Hypercard, Highlighted Data says it gives users instant access to 17,000 individual files on Congress. Punch in a subcommittee name, and CongressStack will give you the members. Punch in a district, and CongressStack will give you a profile of the representative.

"It used to take mass mailers days to develop specific committee-by-committee mailing lists. With CongressStack they can do it in an afternoon. I don't know whether that's good or bad for members of Congress, but it sure will make life easier for the lobbyists," Barker said.

CongressStack isn't the only computerized guide to the Hill. Washington's Sunshine Services sells an IBM-compatible software package known as Elect, which lists mailing addresses, office phones, districts and party affiliations for members of Congress.

At $35, Elect is less expensive than CongressStack, which retails for $159.95. But Barker said other programs haven't the capability of CongressStack. "None of the others have maps, boundaries, pictures and zip codes," said Barker. A user can edit, update or add new information to CongressStack.