Mitch Kupchak, substitute turned millionaire, will be among the five highest paid players in the National Basketball Association when he starts working for the Los Angeles Lakers next season.

When all the loose change is added up, the 27-year-old former Washington Bullet forward will earn about $8 million with the Lakers and have a tremendous opportunity to add millions more through investments.

"Yes, you could say that Mitch's contract is in the top five in the league," said Larry Fleisher, the New York attorney who negotiated the deal with Lakers' owner Jerry Buss. Fleisher also is the legal counsel for the NBA Players Association and has access to every player's contract.

Two clauses in Kupchak's contract have not previously been revealed:

After his original seven-year, $800,000 annual contract has expired, he goes on a personal-service contract worth $325,000 a year for the next seven seasons.

As soon as he officially signs his contract with the Lakers, he will be paid $500,000 of his first year's salary in cash, which he can invest immediately.

"The ideal investment, of course, is real estate, something that will give him a tax shelter," said Bob Lewis, an investor with Johnston Lemon & Co. "If Mitch could get a tax exemption that would yield 10 or 11 percent tax free, that would be better than the 17 percent fully taxable return he would get in a money-market certificate. But even if he simply put it in certificates, he could make $85,000 the first year on interest alone."

In each of his seven seasons, Kupchak will have 30 percent of his salary deferred -- the maximum allowed under the latest NBA regulations.

Kupchak signed a five-year contract worth $160,000 a year with the Bullets five years ago after graduating from North Carolina. He averaged 12.1 points a game and eight rebounds in a reserve role.

"I've never had much chance to do any investing," Kupchak said. "A lot of my money has been deferred (half his $160,000 salary), and after I bought two houses and a new car, well I had, maybe, one gas and oil deal a year.

"I have a man in Atlanta that Coach (Dean) Smith (of North Carolina ) introduced me to that has been handling my affairs. I guess I should be all right now."

All right to Mitch Kupchak means a clean pair of jeans, a full supply of shoes and enough T-shirts so he doesn't have to do his laundry more than once a week.

A bachelor, he prefers a simple life style, although that could change in Los Angeles.

"This deal couldn't happen to a greater guy," said General Manager Bob Ferry of the Bullets, who confirmed the figures and clauses in the offer sheet from Los Angeles. The Bullets countered with $500,000 a year for five years, which would have made him the highest paid player in the history of the franchise.

"Here is a genuine person, a 100 percenter in effort, determination and off-season work," Ferry said. "He's always worked hard and never complained. He's one of the few players in the world, when he gets a deal like this, nobody is resentful.

"Two years ago, he was lying in a hospital about to undergo a second back operation, and after all the mental anguish he went through, I'm very happy this has happened to him."

What has happened, of course, is that after waiting patiently behind two of the most durable standouts in NBA history, Elvin Hayes and Wes Unseld, Kupchak will get a chance to start on one of the best teams in the league.

"We've been very interested in Mitch for a long time," said Bob Steiner, the club's director of public relations. "I would say that we contacted his attorney at the first possible date.

"The position we were drafting (19th), we knew we weren't going to get a quality power forward. We discussed the players available and unanimously decided on Kupchak."

Fleisher described the negotiations with Los Angeles as "long and complicated," and said one reason they were so delicate was because of Kupchak's desire to stay with the Bullets.

When asked about the unusual personal-service clause, Fleisher admitted that it was brought up by Buss and "that's not something I would generally initiate."

Buss, a self-made millionaire, earned a doctorate in physics and chemistry from the University of Southern California and once was headed for a life in academia. He understands money and how to use it.

He first came onto the sports scene when he purchased the Los Angeles Forum, plus the basketball and hockey teams, from Jack Kent Cooke for $67.5 million in June 1979.

"Jerry wasn't the highest bidder on that deal," Steiner said. "But his deal accrued more benefits to Cooke, more value for his money. That's one of Jerry's strengths."

Although he refuses to renegotiate contracts, Buss has made headlines with his recent financial dealings with Kareem Abdul-Jabbar and Magic Johnson. In addition to paying his superstar center $1 million a year, he gives Abdul-Jabbar the Forum rent-free two nights a year for concerts.

Johnson just received the biggest contract in sports history, $25 million over 25 years. Later it was revealed that Buss purchased a $5 million trust deed, presumably to a piece of real estate, for Johnson. The interest from the 20 percent mortgage comes to a cool million -- or Magic's salary when his new contract becomes effective in two years.

"Buss is a brilliant guy, but he's a regular guy, too," Ferry said. "He didn't want to hurt us on this deal. He really wanted to make sure he gave us something in return. I really believe that."

Although Bullet owner Abe Pollin couldn't match Buss' offer for Kupchak, the Lakers made a trade, giving the Bullets veteran forward Jim Chones, reserve guard Brad Holland, a No. 2 draft choice in '82 and a No. 1 pick in '83. When asked why, Steiner had a simple explanation.

"We never considered not trading for Mitch," he said. "We didn't want to bury Washington. He wanted to give the Bullets something in return. But most of all he wanted Kupchak, and he usually gets what he wants."