If nothing else, Wall Street is endlessly inventive, continually finding unexpected ways to shake Americans’ faith in the stock market.

The latest is the brouhaha over the $139.5 million the New York Stock Exchange is paying its chairman and chief executive, Richard A. Grasso.

As scandals go, it’s not up there with Enron and WorldCom. But there are so many things wrong with this, it’s hard to know where to begin.

While the NYSE clearly hoped the outcry would quickly die after the pay package was announced Aug. 27, this doesn’t look likely. On Tuesday, William H. Donaldson, chairman of the Securities and Exchange Commission, sent the NYSE a sharp letter demanding a detailed explanation for the payment.

Grasso has been paid more than $10 million annually for several years. The exchange says the $139.5 million is compensation that he had deferred — and on which he was guaranteed an 8 percent annual return.

The most obvious problem is the extraordinary amount of money, which the exchange says is meant to keep Grasso at the level of top Wall Street executives.

But there’s no reason that should have been the goal.

Many Wall Streeters and corporate executives are obscenely paid, and the scandals of the past few years are rooted in the culture of greed at the top. The exchange shouldn’t be mimicking that behavior; it should be discouraging it.

Even if you think top corporate and brokerage executives deserve their riches, there’s no reason the head of NYSE needs to run in that crowd. Under the supervision of the SEC, the exchange is the regulatory organization overseeing the 2,800 companies whose stocks are traded on the exchange.

Umpires aren’t paid as much as the pitchers and batters they referee. Judges don’t make as much as the attorneys who appear before them. Indeed, the SEC’s Donaldson earns a mere $142,500.

The NYSE is a corporation owned by the companies whose stocks are traded there, and one could argue that they have the right to overpay if they want to — though their shareholders might think otherwise.

But the exchange also is a public trust. If you own stocks, invest in mutual funds or depend on a pension that holds stocks, you have a right to expect the NYSE is looking after your interests. The NYSE should be working to reduce the corrupting influence of excessive executive pay, and it can’t do this effectively if it’s playing the game itself.

The exchange is not wealthy — it earned just $11.6 million in the most recent quarter. Its money should be spent on regulatory and oversight functions, not lavish pay for insiders.

Historically, the exchange has failed to live up to the disclosure requirements it imposes on its member corporations, and this is the first time its chairman’s pay has been made public. In his letter, Donaldson complained, quite rightly, that the NYSE had not responded fully to a request he made in March that it review its own governance.

Indeed, the exchange’s efforts to improve the governance of its listed companies have been unimpressive.

Finally, the 8 percent annual investment return Grasso was guaranteed on deferred earnings was clearly excessive. At most, a guaranteed return should match what one can get in safe havens such as bank savings or U.S. Treasury bonds. The benchmark 10-year Treasury has yielded between 3.5 and 6.5 percent since 1998, when Grasso’s 8 percent guarantee began.

And during that period, the average stock, as measured by the Standard & Poor’s 500 index, has returned a mere 2.0 percent a year — one-quarter what Grasso got.

As head of the largest stock exchange, Grasso should share the fate of the millions of stock market investors. Instead, he got a sweetheart deal.

He’s just another fat cat who got richer as ordinary folk got poorer.