The Media Institute, a corporate-and foundation-sponsored research group dedicated to correcting the errors in the ways of television coverage of business and economic issues, last night celebrated moving into new offices in Georgetown.

"It's a joyous occasion for two reasons," said Institute president Leonard Theberge as the raucous sounds of the Federal Jazz Commission all but drowned out his words. "That we're alive after a year and a half and that we have a lower rent.

"The Media Institute is actually four years old, but was essentially dormant until last year," Theberge said. "It's fairly obvious that television coverage of economic issues is abysmal," he explained. "Our goal is to improve the level of coverage with responsible criticism."

As an example, he cited a study the Insititute sponsored of the way the three major networks covered inflation over a two-year period. The study found that government spokesmen and government information dominated the news about inflation.

"Where the government dominates the news in other areas, journalists are quick to point out where the snow job is coming from," said Theberge, who thinks that coverage would benefit by seeking out more spokesman from labor, industry and the academic community.

A study of network coverage of the nuclear industry over a 10-year period (the Institute's researchers used the Vanderbilt University collection of news program videotapes and film) found "shockingly little coverage," and said most of it tended to be "fearful." The coverage tended to encourage "nuclear phobia," the Insitiute said, by asking unaswerable questions in the "what-if syndrome."

Although Theberge maintains that the Institute is nonideological, it would appear to be somewhat conservative in drift, or at least corporate-oriented. About 30 percent of this year's $550,000 budget comes form corporations such as Mobil Oil and Twentieth Century-Fox. Another 60 percent of the funding comes from four foundations, of which Theberge would name only one, the Scaife Family Charitable Trust.

"It annoys the heck out of me that your source of money answers the question of credibility rather than your work prouduct," protested Theberge, a lawyer.

"They intend to do serious research into various structural aspects of the press," said Herbert Schmertz, the man behind Mobil Oil's "fable" television commercial. Schmertz is on the Institute's board. Its advisory council includes former Nixon communications director Herbert G. Klein, reporter Ford Rowan and consultant Bryce N. Harlow.

In one room a videotype produced by the 4,000-employe Illnois Power Co. got serious attention from one small group.Company spokesman Howard Deakins said that he and two co-workers used the company's training film equipment to record a visit by CBS' "60 Minutes" team when it came to do an expose. They taped the segment that was aired, which Deakins said was a totally unfair story, and in one week edited their four hours of tape into a 42-minute rebuttal. They said it cost about $89, including two dinners.

The power company film shows what CBS ran followed by additional information from the company or additional footage from an interview. Deakins said that the company, based in Decatur, Ill., has been deluged with requests from companies all over the world as well as journalism schools, and that more than 2,000 copies of the rebuttal tape are now circulating. The Media Institute has about 75 copies that it loans out in a kit complete with transcripts and CBS responses.

The major television personality who attended last night's gathering was NBC correspondent Richard Valeriani, who does not cover economics but was nonetheless somehow pressed into the position of defending his industry. "Economics is the kind of story that's very difficult for TV," he said. "How do you communicate it?There's statistics, it's enormously complex, and you have to have some kind of visual. I think Irving R. Levine [NBC's economics reporter] is quite good."