Interior designers are space planners. They calculate how much room a client company will need and figure out the best way to configure the area for maximum efficiency for that particular type of business. Although they do some work in rehabilitated buildings, they prefer to design the inside of a new office while it is still on the drawing board.

All of the designers in the group interviewed by The Washington Post work exclusively with private corporations, not the government.

Interior designers claim they can save a business hundreds of thousands of dollars in rent for otherwise excess space through their planning. For this they receive compensation based either on square footage or an hourly rate. A typical fee is $2 to $3.50 per square foot, or about $25,000 for an average size company. The hourly rate is typically 2 1/2 times the hourly wages of the professional involved. An architect might bill $65 an hour. Some designers receive a commission on the furnishing they buy for the client; others merely make recommendations.

There are perhaps 15 major business-interior design firms in the affluent Washington area. But as private industry expands here, there is a growing tendency to employ designers from elsewhere in the country.

When First American Bank decided to redo its main office and open a branch at Connecticut and Van Ness NW, they turned once again to the Friday Design Group, which had done work for the bank for years. First American Senior Vice President Francis Curtin recalled, "We just told them what we wanted," how many automated teller machines and how many employes. The firm came up with preliminary drawings that required very few revisions.

Curtin, who has overseen the construction of 15 branches, described his philosophy. "I want it to look nice. I don't know what the style is. Just as long as the colors aren't green and purple. They came in on budget and on time. That's I'm paying them for."

Contrast the bank's approach with that of the law firm Arnold & Porter when it decided to go into brand new offices. First it compiled a list of 15 design firms. The principals were interviewed and the list narrowed to three. These were interviewed in depth and the search committee visited some of the interiors they had created.

Ultimately, Environmental Planning & Research (EPR) of San Francisco was selected. The design firm did psychological profiles of 140 partners and associates and questioned the supervisory and operating staff on their preferences.

Most of the lawyers wanted something completely different from the traditional law office. They chose a contemporary style, very light and airy, with lots of public space to display the firm's modern art collection. There are seven different office shapes and sizes, the largest being 300 square feet.

Each partner received a certain number of hours of EPR time to discuss his or her decor, plus an allowance for furnishings. Several lawyers preferred to hire their own decorators. Associates were given three options on furniture, fabric and office configuration.

As a result, the individual offices contain such disparate furnishings as a lucite desk and an old-fashioned slatted wooden chair, a brass hat rack and Oriental rugs. Yet the overall effect created by the common areas is highly contemporary.