MICHAEL Doonesbury has my sympathy. Gary Trudeau's cartoon leftist-turned-blow-dried-Yuppie is wrestling with the classic liberal dilemma.

In the current series of Doonesbury strips, Michael's employer wants him to design advertisements to lure first-time, or "entry-level" smokers into a lethal habit. The contract promises big money, but his liberal soul protests. Should he serve God or Mammon--social responsibility or individual opportunity?

I, too, wrestled with temptation, and temptation won handily.

THIS week, The New Republic carried a critique of the Princeton Review, a company that employs me to teach rich suburbanites how to beat the Scholastic Aptitude Test (SAT). The article asserts that the Princeton Review doesn't really improve students' qualifications for college but teaches them to "beat the test" without actually knowing the answers. The Princeton Review course, it says, allows wealthy students to exaggerate their qualifications for college, thereby gaining an advantage in admissions over equally talented students who can't afford the $645 fee.

This is all quite true. By teaching for the Princeton Review, I am effectively squelching opportunity and raising barriers to disadvantaged students. It's ethically dubious, but I need the cash.

In the abstract, making money through unethical actions is reprehensible to a liberal's conscience. When posed as a hypothetical choice--principles or money--the decision is easy. But in reality, $15 per hour weighs heavily against abstract principles.

Apparently, not only are my principles for sale; they're quite a bargain.

THIS Ivory-Tower paradox disturbs me enormously. How can I advise readers, say, not to take advantage of Eastern's money-saving fares just because "it would be wrong," when I can overcome ethical qualms in an exactly analogous situation. How can I justify condemning those who invest in South Africa for profiting from institutionalized racism when I am earning money through an ethically questionable business?

I could defend myself by saying that my ethical failings are somehow not as qualitatively reprehensible as, say, dumping toxic waste for profit. But if the deeds are not equally heinous, the violations of principle are. Either you believe that right supercedes riches or you don't.

Like thousands of 60s leftists turned 80s salary-earners, I don't believe that money-making is inherently bad. But neither should it be a summum bonum. Individual profit-seeking must be weighed against a larger social good. That's why we condemn Ford Motor Company for its combusting Pinto and Frank Lorenzo for his union-busting.

But to actually obey the standards that I righteously hold up for others is more difficult, especially since the rationalizations that I offer for my own actions are identical to those used by the profit-lusters I detest.

I wouldn't do it if I didn't need the money so much. For precisely the same reason, Brazil allows the decimation of its rainforests and auto manufacturers resist pollution control.

Even if I didn't do it, someone else would. It might as well be someone who at least knows it's bad. A perfectly specious argument that liberals regularly condemn in the likes of a certain university that refuses to divest of its holdings in firms that deal with South Africa.

It can't be that bad. There is, after all, a certain logic to the free market that assures the best possible... That's exactly the point. Because it does not make ethical judgments, the market cannot be counted on to encourage socially desirable decisions.

What's worse, it penalizes those who respect ethical distinctions. Mike Doonesbury and I follow our consciences at our financial peril.

But regulating market activity is not an adequate solution. It only works to control activities that are actually destructive, such as environmental pollution and corporate negligence. SAT prep courses, though they perpetuate an injustice, cannot be legitimately prohibited just because they are morally unpalatable to some.

FOR those morally questionable activities that are technically legal, we are left with a wholly unsatisfactory solution. We could pursue complete ethical purity in economic affairs. But such a course is entirely impractical. The market seldom rewards moral uprightness. Alternatively, we can attempt to distinguish among varying degrees of ethical corruption and weigh them against financial gain, leaving the individual's greed as the final arbiter.

Unfortunately, in the myriad conflicts between principles and money, there is no obvious place to draw the line. I still can't decide on which side my Princeton Review work falls. But if I ever save enough money, maybe I'll quit.