NEW YORK -- Gatsby he is not, but he, too, dreamed the same golden dream.Like many others of his age and time, Thomas Melendy was on his way up, with high expectations of profiting personally and professionally from the boom. Single, 26, confident, he viewed the future with unbounded optimism. Here he was, only two years out of business school, on Wall Street and about to purchase what surely would be the first of many fine possessions, a loft apartment priced around "160 grand."

Now, suddenly, shockingly, he's out on the street. All of his life plans are altered. The bell has tolled for him and perhaps for many like him in the Yuppie generation.

"I had been with the firm for over two years, and we work on all the accounts, deal with the brokers, make sure the margin is correct and, when the big crash came last Monday, we worked all weekend," Melendy was saying while idly browsing through a bookstore near the American Stock Exchange and the big brokerage house that was his first employer. "You would have thought that, even with the crash, we would have been needed to take care of the extra paper work and send out all the calls and everything.

"I thought the market would recover sufficiently enough. It gained back, I think, 250 points last week, and I have a spotless work record, always come in on time. I think I've taken one out of my six personal days, two of my 10 sick days. I had no inkling what was coming.

"So this Monday, three people from each operations department, including myself, were called to personnel and told we were terminated. That was the word used. Terminated. And, you know, it's a horrible feeling. Eight weeks from Christmas. You know you're being done out of a big bonus. And you have a lot of friends. There are 50 people in the office where I work, spend eight, nine, 10 hours a day, 40 to 50 hours a week. It's a good part of your life. I went to the bathroom and cried."

Melendy is part of a statistic that underscores the magnitude of the wreckage of the stock-market crash and that perhaps marks the passage of an era.

Experts are predicting that the crash will result in the elimination of one-fifth or more of Wall Street's work force by the end of next year. Ultimately, as many as 50,000 people might lose their jobs. Among them will be many of the high-flying young financial superstars of the '80s, who have come to count on bonuses ranging upward from $100,000 and salaries of six, and even seven, figures. This bounty has been achieved while they're still in their 20s.

Whether the country will weep for displaced Yuppies is doubtful. More likely, cheers will signal their demise. Fair or not, the image of swaggering, grasping, greedy, uncaring young professionals on Wall Street has taken hold strongly nationwide, and for good reason.

Aside from natural resentment at their inflated salaries, their gaudy life styles and singular drive for more and more material possessions, the country long has wondered just what these hotshots really were producing and at what relevance to genuine national wealth.

The more important question is: Why in recent years have so many bright young Americans chosen to work for private gain instead of public interest, for celebration of self rather than service to others?

If any lesson emerges from the disasters produced by Wall Street's let-'er-rip, live-for-now, get-mine mentality and Washington's permissive, let-the-deficits-bloom political climate in the Reagan era, it is that the country no longer can afford business as usual. It needs the best talents of its best people working cooperatively in the best interests of all Americans.

"The Yuppies, the materialism of these kids, I think that's gone now," a senior Wall Street executive said, reflecting on the aftermath of the crash. "I don't think you're going to see 80 percent of the graduating class want to come into the securities business. In fact, I don't think it's the sign of a healthy society when so many graduates go into Wall Street. I would like to see them become rabbis and doctors and go into the Peace Corps and write music or do other things."

The crash might just help bring about that kind of welcome change in aspirations. Thomas Melendy's present state of mind suggests such a reassessment already is taking place.

His pre-Wall Street dream had been to become a filmmaker.

"I may wind up going back to filmmaking," he said. "It's something I love. I certainly like it a lot more than making money for other people, you know."