Now that you have distinguished yourself morally from people who put their vintage cars ahead of a child's life, how about treating yourself and your partner to dinner at your favorite restaurant? But wait. The money you will spend at the restaurant could also help save the lives of children overseas! True, you weren't planning to blow $200 tonight, but if you were to give up dining out just for one month, you would easily save that amount. And what is one month's dining out, compared to a child's life? There's the rub. Since there are a lot of desperately needy children in the world, there will always be another child whose life you could save for another $200. Are you therefore obliged to keep giving until you have nothing left? At what point can you stop?

Hypothetical examples can easily become farcical. Consider Bob. How far past losing the Bugatti should he go? Imagine that Bob had got his foot stuck in the track of the siding, and if he diverted the train, then before it rammed the car it would also amputate his big toe. Should he still throw the switch? What if it would amputate his foot? His entire leg?

As absurd as the Bugatti scenario gets when pushed to extremes, the point it raises is a serious one: only when the sacrifices become very significant indeed would most people be prepared to say that Bob does nothing wrong when he decides not to throw the switch. Of course, most people could be wrong; we can't decide moral issues by taking opinion polls. But consider for yourself the level of sacrifice that you would demand of Bob, and then think about how much money you would have to give away in order to make a sacrifice that is roughly equal to that. It's almost certainly much, much more than $200. For most middle-class Americans, it could easily be more like $200,000.

Isn't it counterproductive to ask people to do so much? Don't we run the risk that many will shrug their shoulders and say that morality, so conceived, is fine for saints but not for them? I accept that we are unlikely to see, in the near or even medium-term future, a world in which it is normal for wealthy Americans to give the bulk of their wealth to strangers. When it comes to praising or blaming people for what they do, we tend to use a standard that is relative to some conception of normal behavior. Comfortably off Americans who give, say, 10 percent of their income to overseas aid organizations are so far ahead of most of their equally comfortable fellow citizens that I wouldn't go out of my way to chastise them for not doing more. Nevertheless, they should be doing much more, and they are in no position to criticize Bob for failing to make the much greater sacrifice of his Bugatti.

At this point various objections may crop up. Someone may say: ''If every citizen living in the affluent nations contributed his or her share I wouldn't have to make such a drastic sacrifice, because long before such levels were reached, the resources would have been there to save the lives of all those children dying from lack of food or medical care. So why should I give more than my fair share?'' Another, related, objection is that the Government ought to increase its overseas aid allocations, since that would spread the burden more equitably across all taxpayers.

Yet the question of how much we ought to give is a matter to be decided in the real world -- and that, sadly, is a world in which we know that most people do not, and in the immediate future will not, give substantial amounts to overseas aid agencies. We know, too, that at least in the next year, the United States Government is not going to meet even the very modest Umited Nations-recommended target of 0.7 percent of gross national product; at the moment it lags far below that, at 0.09 percent, not even half of Japan's 0.22 percent or a tenth of Denmark's 0.97 percent. Thus, we know that the money we can give beyond that theoretical ''fair share'' is still going to save lives that would otherwise be lost. While the idea that no one need do more than his or her fair share is a powerful one, should it prevail if we know that others are not doing their fair share and that children will die preventable deaths unless we do more than our fair share? That would be taking fairness too far.

Thus, this ground for limiting how much we ought to give also fails. In the world as it is now, I can see no escape from the conclusion that each one of us with wealth surplus to his or her essential needs should be giving most of it to help people suffering from poverty so dire as to be life-threatening. That's right: I'm saying that you shouldn't buy that new car, take that cruise, redecorate the house or get that pricey new suit. After all, a $1,000 suit could save five children's lives.