The air conditioning hadn't found its way downstairs to the Hilton's Crystal Ballroom. One woman fanned herself and complained, "It's so hard to be elegant when it's this hot." But Irving Schwartz was happy. "This is the greatest convocation of interior designers in the history of the world," he exulted.

Schwartz smiled. "We're interior designers," said the architect and designer from Champaign, III., who is president of the American Society of Interior Designers, gathered 2,000 strong in the ballroom and celebtating over the weekend at their annual convention with a '50s-style dance.

Once upon a time, Schwartz said, architects were trained as interior designers. But after the 1930s, architects following the lead of Walter Gropius and Ludwig Miles van der Rohe began to put up low-cost buildings that were designed as space - living space, office space, it didn't matter. That's when the term "interior decorator" came into use. "Someone to pick out the couches and the pictures on te wall," as Washington designer Kent Slopicka put it somewhat derisively. Architect Frank Lloyed Wright put it even more strongly - he called them "inferior descraters."

"We've not trying to put any architects out of business - we're just trying to say, look, the space isn't complete until the furniture is put in." said Schwartz. "You can go all over Washington and find buildings where wires are taped across the floor, where the telephones won't reach the desks, where the lighting is no good, all because the architect didn't know enough. We want them to work with us."

Schwartz was getting ready to go on the '50s dance, and, in costume, he took a cigarette out of the package rolled up in the sleeve of his champray shirt. "Did you know the cigarette is the cause of 90 percent of the fires related to furniture?" he asked. "That's the kind of thing a designer has to plan - flammability standards, signs, the entire space."

"I think of it as a service delivery system," said Dr. Edward R. Ostrander. "Once upon a time the interior designer was simply an arbiter of taste - if somebody said, 'Hey, I want a Louis XIV room,' he went and did it. But now he has to ask, 'What are you trying to accomplish?' and deal with whole space."

Ostrader, a rumpled man a red-white-and-blue-checked jacket, is a psychologist who teaches design at the New York State College of Human Ecology at Cornell. He was at the convention to talk about "the needs of users. How does a 24-year-old male designers plan a bathroom for an 84-year-old arthritic woman? He's not a woman, he's not 84, and he's not arthritic - how does he deliver the service?"

He shook his head. "Too many times, nobody thought about that," Ostrander said. He shook his head. "This industry and the car industry - it's like the recalls of automobiles. The only industries I know where the consumer is also the test base. But we'll fix it." He grinned.

Meanwhile, Slopicka and John Berry of Detroit were just finishing a workshop on signs. "Signs are very important to the interior designer," Slopicka said. "Like that sign over there," he added, pointing to the standard red EXIT sign over the door. "Very poorly designed sign. If this room fills with smoke, I won't run towards a red glare. I might if it were green."

"The big thing," said Slopicka, "is to get the interior designer on the team. An architect won't overlook the electricl engineer or the structural engineer, but he might overlook the interior designer. And an interior designer is someone who comprehensively plans the interior."

"An interior designer is a problem-solver," interjected Berry, " and an interior decorator is a mood-maker."

"Right - but you won't hear anybody referring to themselves as an interior decorator," Slopicka added. "Everybody's an interior designer." They both laughed.

"Downstairs, the exhibition was about to open. Sonya Kelley, wearing a black dress, fanned herself but smiled.

"Back home in Nashville the clients get to you and you get fed up - these conventions are like a shot in the arm," said Kelley, a designer for 11 years.

"But it's stimulating work," she added. "It's really not decorating any more. Ever since I was little I've liked fooling with my environment, and I guess that's why I got into it. Now I deal with the total living environment, a system."

The exhibition - 500 displays from around the country - had opened, but things were a little slow in front of Colleen Vogel's booth. A woman whose business card identifies her as Topsy Vogel stood in front of a display of Pinecrest doors.

"A solid mahogany door," Vogel said, and rapped on it. "People build a house and put in gold faucets and put the rattiest door out front. A door is the first and last thing visitors see - in Europe they're always known that."

When things got slow at the Gayeski Furniture booth. Frank Gayeski would nonchalantly spill some Cutex on the top of one of his executive desks and set it on fire. It never failed to draw a crowd.

It never failed to make Charles DiBlast laugh, either. DiBlast was the man responsible for the finish on the flameproof line of Gayeski office furniture. "It's a polyester finish over burl," said DiBlast, "looks like marble, damn near as hard, and there's no stain." The last crowd of onlookers moved away, and Gayeski reached for the Cutex bottle again.

Eileen Kay of Rockville and Ingrid Stead of Annapolis strolled the exhibit floor. Students at the International Institute of Interior Design, they were among about 200 students attending the convention, a little wide-eyed - "Just getting our feet wet," Kay smiled nervously.

"Television," said Stead, "television told people they could live better. Cost them a little, but they could live better."

"I've learned a lot here," Stead announced. "I'm going to do residential designs, but some commercial too - after all, there's more money in that. But I want to deal with . . . whole space," she said finally and grinned.

"I do too," said Eileen Kay.