DETROIT -- Nearly a year after his dramatic ouster from the board of General Motors Corp., Texas billionaire H. Ross Perot sees GM in turmoil, its sales plunging and the company drifting and leaderless. And he thinks he knows why.

As always, 57-year-old Perot isn't shy about telling the world what he thinks.

GM is troubled, Perot said, because it is beset by power-hungry top executives who spend their time trying to move up the ladder and who do little to improve the quality of GM's cars.

"My greatest regret is over the maneuvering and politics and power-grabbing going on inside the corporation, which distracts them from making the finest cars in the world," Perot said in an interview.

"Too much energy is being used up in corporate in-fighting. The corporation ought to be devoting its energies to making the finest cars in the world, and not get tied up in management power struggles and Machiavellian intrigues, and that's what is going on. It's sad to see."

And despite the threat of multimillion-dollar fines for making negative public comments about GM -- a provision of the $700 million buyout agreement Perot signed when he sold his huge GM stake back to the corporation last year -- he also is willing to identify who he thinks is the chief villain at GM.

It is Elmer Johnson, a GM executive vice president widely reported in Detroit to be mounting an intense drive to succeed GM Chairman Roger B. Smith, who is scheduled to retire in 1990.

Johnson is a 55-year-old former corporate attorney from Chicago who has been at GM for four years and who joined the company with no experience in the auto business.

He started as general counsel in 1983 and since has seen his responsibilities expanded to include a broad range of staff functions, including public affairs, personnel and labor relations. He was the executive overseeing this year's contract talks with the United Auto Workers.

Perot believes Johnson, who was also the point man for GM in the company's efforts to oust Perot, is representative of a larger malaise in GM management, which he believes is paralyzed by corporate politics.

"Elmer is clearly maneuvering for power," Perot said. "Elmer has been busy for months tooting his own horn, allowing himself to be photographed playing his saxophone {actually a trumpet} on the cover of the Detroit Free Press Sunday magazine... . The last thing GM needs is an executive with his feet on the desk on the 14th floor {the top corporate suite in the GM headquarters building} who doesn't know how to make a car.

"GM cries for an executive with both feet on the factory floor who knows how to make a car. Only in America could a man who was Playboy's lawyer think he could become chairman of the world's largest automobile company."

(One of Johnson's Chicago legal clients was Playboy Enterprises President Christie Hefner).

"But you've got a giant organization that's not functioning well, and there you go. People sense weakness, and step in and try to take control," Perot said.

Johnson and other GM executives declined to respond to Perot's comments last week. "There is nothing to be gained by responding to Mr. Perot's comments," said GM spokesman Jim Crellin.

Smith and other executives have tried to limit the damage from the Perot affair and have taken steps during the past year to boost GM's tarnished image.

Several months after Perot's ouster, Smith launched a public relations offensive, wooing Wall Street analysts and investors as well as the news media. He sent letters to the company's stockholders stressing the firm's effort to build better cars, and last week told reporters he sees the 1988 model cars as the key to regaining lost market share.

Even Perot says he has been pleased by GM's effort to improve communication with stockholders as well as by the company's decision to replace its executive bonuses with a compensation package tied to corporate achievement.

Still, Perot has neither forgotten nor forgiven GM for its actions in late 1986. And a year later, he hints that he still doesn't completely understand why it happened.

A flamboyant superpatriot and self-made billionaire, Perot sold Electronic Data Systems, the Dallas-based computer services company he founded, to GM for $2.5 billion in 1984 and immediately became GM's largest shareholder and a member of the board.

He sold his privately held company only after Smith persuaded him that GM needed EDS to help in the auto maker's drive to become a world leader in factory automation, and likewise needed Perot's fiery spirit to reinvigorate GM's bureaucracy for the big battle with the Japanese.

But it didn't take long for Smith to realize Perot was really too fiery and was becoming a loose cannon in one of the most tradition-bound corporations in America.

Perot questioned longstanding management practices, and openly sought to stir things up.

He would go to the factory floor to talk to workers about new ideas and would anonymously shop at GM dealerships, trying to gauge customer service.

On the board, he provoked Smith when he became the only member to vote against GM's $5.2 billion acquisition of Hughes Aircraft in 1985.

Most importantly, he refused to turn over the reins of EDS completely to GM.

Because EDS remained a separate unit under GM, Perot demanded GM meet its contractual obligations to EDS for the computer subsidiary's work in GM facilities.

He said EDS had to show real profit in its business with GM to guarantee that its stock, GM Class E, would retain its value.

Smith tired of Perot and briefly considered selling EDS to AT&T, apparently in part to get rid of Perot.

When that didn't work, GM decided to buy Perot out. On Dec. 1, 1986, GM announced that Perot was resigning from the board and that the company was paying him about double the market price for his GM stake.

Now, Perot says he remains busy in his hometown of Dallas, overseeing his massive investments, which include Texas real estate and oil and gas properties.

He is biding his time until May 1988, when he will be free, under the terms of his GM buyout, to build a new EDS and hire anyone from his old company that he wants.

He said he would found a new computer services company to compete with EDS only if his "guys" -- his loyalists still at EDS -- are unhappy with GM next spring.

He adds that he is generally pleased that GM now seems to be living up to its contractual agreements with EDS.

''I'm not going to push it or encourage it; it's in GM's hands,'' he said. ''If the guys are still happy, we will forget about it and we won't do it."