An ugly little incident in the streets of Manhattan three nights before the New York mayoral election helped explain a faintly understood byproduct of the long campaign: the establishment of the city's organized homosexuals as another pressure group to be appeased by politician.

The incident involved campaign workers putting up posters for Liberal Party candidate Mario Cuomo, who belatedly had broken with the homosexual movement. The Cuomo workers were pushed aside by self-styled "gay" activists, who pulled down the posters. It was not the first instance here of homosexuals resorting to physical force.

That is one reason by practical politicians believe Cuomo may be New York's last serious candidate to even hint at challenging homosexual political legitimacy. "It is a loser, believe me," one experienced politician, soon to be waging a campaign here, told us. Thus, a sexual aberration traditionally rejected by Western values takes its place in New York, as it did previously in San Francisco, beside racial and ethnic groups as a political "minority" to be courted by politicians.

This development was obscured by a political irrelevancy: the vicious, factually unsupported whispering campaign that the victorious mayoral candidate, Rep. Edward I. Koch, is homosexual. Actually, politicians know Koch's surprisingly small victory margin was caused not by smears but by Republican voters abandoning their own candidate for Cuomo.

Even if Koch did lose support on the homosexual issue, it was not because he unequivocally endorsed the "gay rights" bill before the city council but because he happens to be a bachelor at age 52. The conventional post-election wisdom is that any future candidate here, particularly if he is a husband and father, cannot lose support and certainly will avoid trouble if he goes along with the homosexuals.

This in part was unintentionally caused by Cuomo, who was labelled the fresh political newcomer who would invigorate the city but proved another good man who is a poor candidate. Indeed, "gay" power might have been blocked as an established pressure group had Cuomo heeded a key adviser: Adam Walinsky, boy-wonder aide to Robert F. Kennedy a decade ago and later Democratic nominee for state attorney general.

Walinsky last spring proposed a three-point Cuomo platform to energize the city's silent majority in the Democratic primary: 1) endorse capital punishment (as Koch did), 2) talk really tough on welfare spending (as nobody did), 3) oppose the "gay rights" bill. For Walinsky, the last point rated Cuomo from his Democratic primary opponents (all firmly supporting the bill) but raised serious questions of what kind of society the government should promote.

Cuomo rejected the advice on all three counts, salvaging his New York Times endorsement while losing the primary. Wilinsky then put his advice on homosexuals into an essay in the June 21 New York Daily News. The "gay rights" bill is a "true threat to human and societal values," he wrote, adding: "There is neither reason nor excuse for my government telling me, and my children, that homosexuality is good or even acceptable."

A few weeks later, about 50 members of the Gay Activists Alliance carrying baseball bats surrounded Walinsky's home in suburban Scarsdale, tossed firecrackers and threatened to burn down the house. When Walinsky tried to call the police, he found his phone lines had been cut.

Militant homosexuals marched in the city's streets a dozen times in October alone - protesting each case an anti-homosexual utterance. The intimidation of New York politicians, never renowned for their moral fiber, was palpable.

Those politicians now talked about an organized homosexual vote of 10 per cent. In fact, it may be half that amount and not organized at all, but image is more important than reality. The advent of gay power was confirmed by a favorable article in the Oct. 25 New York Times under the headline: "Homosexuals in New York Find Pride."

It was then, improbably, that Cuomo began to worry aloud that the "gay rights" bill might enable homosexual proselytizing in the school room, just as Walinsky had warned six months earlier. But by not making clear that expansionist homosexuality threatens the society, he seemed a desperate politician aiding a reprehensible smear campaign.

Fuzzy though it was, Cuomo's criticism was intolerable for the organized homosexuals, who began ripping down his posters. That response, plus election post-mortems equating legitimate concern over homosexual activitism with illegitimate personal smears against Koch, shapes the future.

Candidates will fulfill political demands of homosexuals as they have for racial minorities, following the New York ground rule that politicians must give to everybody but take from none. That rule so far has brought the city to economic collapse. Now, applied to the homosexuals, it threatens the perception of New York by its remaining middle-class residents as a place where traditional values can be preserved.