It used to be said that sex, politics and religion were the subjects you should avoid if you didn't want to get into a shouting match. I would add to the list New York City - its plight and its prospects for salvation. The mere mention of the subject can detonate an otherwise tranquil Washington social occasion. And, as the angry exchanges between New Yorkers and practically everyone else over the meaning and message of the recent blackout demonstrate, we are not much closer to a consensus on who should do what for the city than we were when its calamities first came to national attention a few years back.

Why should this be? Because, I think, we are all walking around with a headful of assumptions, illusions and prejudies that add up to an idea of New York City, as distinct from the reality. And these can get in the way of dispassionate thought and action. To generalize outrageously (but usefully, nevertheless), you could say that there are three basic ideas of the city in conflict at the moment: that of the outlander, that of the New Yorker and that of the folks in Washington who preside over the national cash register. Until these ideas are reconciled in some measure, you just aren't going to get a serious, fundamental attack on New York City's troubles.

For the outlander - I speak as one born and bred - the idea has always been made up in equal parts of awe and suspicion: curiosity, reverence, excitement and resentment rolled into one. New York had (has?) more of everything and better too, a fact its residents were never shy about asserting to the rest of the land. Somehow it was acceptable, forgiven. The folklore was powerful: Broadway shows and lippy cabdrivers and things called automats and an elegant, skycraping, dinner-at-8 world that looked just like the illustrations on the sheet music.

Surely the ancestral memory of all that lingers in the most devoted anti-New Yorkers now. But it is diluted by increasingly powerful images of ugliness, helplessness and disorder. And although some part of the provincial heart seems to be moved to sympathy and a desire to help, there is plainly also an element of smugness and satisfaction at play - well, well, look who's in trouble now: Mr. Bigshot. Moreover, some of the tableaux to which New Yorkers call attention, with a view to demonstrating their problems and enlisting people's aid, are so terrifying as to have the opposite effect. The economic and social Hiroshima that is the South Bronx repels attention and sets the non-New Yorker off on an intellectual effort to persuade himself that that has nothing to do with him - is not his problem, his fault or, if he lives in a city, his future.

So there is, naturally, a tendency on the part of non-New Yorkers to minimize their own interest in the city's recovery. And, humankind being humankind, there is an even stronger instinct to ignore the extent to which New York is having to deal with people who fled to it because they were being systematically mistreated elsewhere. But whatever chance there is that people outside New York will take a generous view of their responsibility to the city seems to me to be threatened by the peremptory, arrogant demands of New Yorkers that Washington and the rest of the nation pay up and get them out of this mess.

And that brings us to the second outrageous generalization: the New Yorker's idea of New York. Like all good provincials who once lived there, for a time I shared it. One begins with this: for millions of people who live in New York, the idea of living anywhere else is ridiculous - not disagreeable, mind you, or just something you'd rather not do, but ridiculous . . . not to be supported . . . unimaginable. This does not make for a whole lot of sensitivity toward the United States of Podunk out there, or generate much reticence about asking the rest of the nation to cough up - which is what it is thought to be there for.

All right, I've exaggerated. But having once shared the amiable contempt for others you can have while living in New York, I would argue that the depiction has its truth. And assuredly that is the impression that prevails in Washington as a consequence of what seems to be an unending series of mean, stormy encounters with some spokesmen for New York City who are continually accusing the government of heartlessness, stupidity and urban genocide. The lights had scarcely gone on in New York when it was being made plain to us here that the looting and damned near everything else were the result of Washington's derelictions as a job and welfare provider, not to mention Washington's responsibility to clean up and remedy.

Or at least that's the way it was perceived on the Potomac - for here we run into the third idea of New York: that held in Washington. The folks who have taken to heart all of the printed claptrap about a Washington-New York axis need to know that although there is a certain amount of beautiful-people traffic back and forth, these are alien, competing cultures. Washington lectures New York on its profligate ways. New York condescends to Washington, makes fun of its pretensions to high living and artistic competence. Washington snarls back that lots of people think it is outdistancing New York on the cultural front. New York convulses with laughter: that is the funniest joke since Albania.

Which it probably is. But the second funniest joke, alas, is the condition of New York politics, a fact that has not escaped notice in this town, where the acquisition and use of political power are considered the highest callings. New Yorks political leadership, with a few exceptions, has atrophied since the grand old days of the New Deal. The city has had, by and large, weak municipal government and uninfluential congressional representation and has seemed to substitute the satisfactions of running against Albany and Washington for those of getting things done in either capital.

New York likes to dwell on its uniqueness. Well it might. The scale of its problems distinguishes them from much that is happening in other struggling cities. But to the extent that its representatives dwell on these distinctions and do so in a condescending way, they only delay the arrival of real help. It's not just that the city stands in danger of being perceived as the nation's no-good brother-in-law, but also that it can repel already skittish politicians from associating themselves with the kinds of policy that in the long run will help save it. There's no amount of money that can buy out New York's problems. They will yield only to concerted efforts to rescue and restore a whole aging quadrant of the nation, long-term measures to reverse the course of industrial migration, profound changes in our tax laws. I get the idea that every day that the city's less-thoughtful spokesmen abuse the rest of the country and holler for more, they put off the day when the right things will be done.