The pessimists, who learn nothing from tragic experience, and the optimists, who sometimes learn too much, are at it again.

The former either feel no urge to seek explanations for disasters - urban riots, prison take-overs, looting and the rest - or they are content to stay with their time-honored villains. The latter give careful ear to each new explanation, then oversubscribe to it as the final panacea.

Both groups are doing their routine in the aftermath of New York City's blackout pillaging.

The pessimists "know" that this social disaster, like all others, has its roots in the fact that some people - individuals or classes or ethnic groups - are animals, and that there is nothing to be done about it.

The optimists insist that there are not only explanations, but solutions. All we need to do is examine the evidence, listen to what those who are involved have to say, persuade the government to appropriate the necessary funds, and we can quickly set things right.

Their notion is that, given the conditions under which some people are required to live (poverty, racism, joblessness and hoplessness), violence and lawlessness are inevitable. Their solutions run to changing the awful conditions.

The pessimists assume that some people simply are no good and that there is no solution except to get tough, lock them in the slammer and do whatever you can to protect yourself from them.

I have a feeling that the pessimists are winning the debate this time. Of course, there are the predictable calls for major assaults on youth unemployment, on substandard housing, on all the social problems. But the calls seem mostly pro forma, in a city unable to pay for even its current level of social services.

The talk one hears in ordinary conversation suggests that the optimists are moving over to join the pessimists in their contention that there is nothing to be done. If the war on poverty and all the special post-riot programs of the 1960s didn't prevent blackout night, isn't it reasonable just to accept these things as inevitable and do what you can to keep personal injury and loss of life to a minimum?

Not quite. In fact the new cynicism is further from the truth than the old faith it replaced.

It is true that government sponsored social programs, whether focused on employment, ethnic pride or generalized assaults on poverty, don't generate social miracles. But it is also true that leaving these problems unaddressed can make things a good deal worse.

U.N. Ambassador Andrew Young aimed in the right direction with his remark that "if you turn the lights out, folks will steal. They'll do it in Switzerland, too, especially if they are hungry."

What he was saying, I think is that given enough darkness (the near-perfect chance of not being caught) and enough hunger (a sense of victimization at the hands of society in general), many of us will take what isn't ours - even if we have to redefine it as ours-by-right.

Some people simply require less darkness and less hunger than others, and for a simple reason: They have less at stake.

What the lack of jobs, the denial of opportunity and the absence of hope have produced is an underclass of Americans who feel that they have nothing to lose. Some of them may be beyond turning around. Protecting ourselves against them may be the only answer.

For the others, hidden in statistics on bad housing, near-illiteracy and unemployment rates at twice the levels of the riot-rocked 1960s, the solution is to see to it that they have a stake in preserving, not destroying, the system.

That it is a long-range - and costly - solution with very little immediate payoff is no excuse for not getting started with it. The costs of not starting are far higher.