Any reporter who knew Martin Siegel during his days as a star investment banker at Kidder, Peabody & Co. could learn a lot from him. Marty, as we all called him, was smart, articulate, accessible, unpretentious, gossipy. His analysis of people and deals was uncanny, and he could explain the most complicated transactions so clearly that anyone could understand them.

Some of my most useful hours were spent joining Marty for frozen yogurt and diet Pepsi lunches -- how do you think he stayed so thin? -- and letting him teach me about what was going on in the world.

Last month, Marty Siegel taught us all one final lesson: that it pays to be a rat.

By being a rat, Siegel, whose behavior I consider to have been the most immoral of all the people caught up in the insider trading scandal, managed to get one of the lightest sentences of any of them: two months.

Compare Siegel's two months with what Lisa Jones got. Jones, a former Drexel Burnham Lambert clerk, got 18 months in jail -- half what Ivan Boesky got -- later reduced to 10 months. Jones was one of the Drexel minions hauled before grand juries as part of the government's years-long investigation of Drexel and its fallen junk-bond king, Michael Milken. Stuck in a grand jury room without a lawyer or the Fifth Amendment to protect her, Jones lied to protect Drexel, and the government nailed her on a perjury charge. It's clear from the public record that the government threw the book at Jones not because of what she had done, but to terrorize other witnesses into cooperating.

Perjury isn't nice, and the government shouldn't let it go unpunished. But let's compare what Lisa Jones did to get 10 months in jail with what Marty Siegel did to get two months.

Jones got into trouble because she was an involuntary witness who lied to protect her employer. Siegel got into trouble because he was greedy.

Siegel, who at the time he began a life of crime was the star mergers and acquisitions man at Kidder, gave secret information about his investment banking clients to Boesky, who paid him with suitcases stuffed with cash. This wasn't some itsy-bitsy technical violation of the securities laws; this was flat-out stealing. Siegel got $700,000 (his version) or $800,000 (Boesky's version) from his crime.

That's not very much compared with the $10 million or so that Siegel turned over to the government. But it was clearly a lot of money to Siegel several years earlier, when he took it. He had just emerged from a divorce, was trying to live beyond his means and was building an expensive waterfront house in Connecticut. It's not as if he and his family were starving, or about to be put on the street.

Siegel's taking the money from Boesky was actually worse than Boesky offering it. Boesky was committing a crime -- but at least he was stealing partly on behalf of his clients, who got a cut when Boesky turned Siegel's information into illicit profits. Siegel not only committed a crime, but also sold out his clients.

When the government nailed him with a subpoena in November 1986, Siegel knew that the feds had him cold. So he ratted on everyone he could, including two former colleagues at Kidder whose only alleged wrongdoing seems to have been acting on illicit information that Siegel gave them without telling them it was illicit.

Then, in a final piece of clever but immoral behavior, Siegel did some fancy shuffling to make sure the people he had betrayed -- his clients and his clients' stockholders -- couldn't clean him out financially after his perfidies became publicly known.

Just before his guilty plea to tax fraud and securities violations was announced, Siegel sold his house in Connecticut and his apartment in Manhattan and bought an ocean-front estate near Jacksonville, Fla. That not only gave him his coveted house on the water, but shielded assets from potential creditors. Under Florida law -- but not under New York or Connecticut law -- Siegel's homestead can't be touched by his creditors if he declares personal bankruptcy.

If you read the pre-sentencing documents submitted by the Justice Department and Siegel's lawyer, you would think the man is a saint. They talk about how contrite he was about his crime, and how much he helped the government.

Contrite my foot. If Siegel were truly contrite, he could have given Boesky the money back. Or he could have confessed before the government caught him. Betraying other people to save your own skin isn't being noble. It's being a rat.

What seems to be going on here is that the government didn't care very much about what Siegel did to other people, as long as he made the government's life easy. Poor Lisa Jones sidetracked the government's investigation of Drexel for maybe 15 seconds by lying; make an example of her. Marty Siegel sold his clients, his honor, his friends and his firm out for money, but he made the government's job easier by snitching. Give him a medal and a two-month sentence.

You can't blame Siegel for trying to cut the best deal possible for himself -- that's what criminals are expected to do. But you can blame a system that gives him two months in jail and Lisa Jones 10 months, and dares to call it "justice."

Allan Sloan is a columnist for Newsday in New York.