THE LARGEST SINGLE BLOC of voters in New York City's June 4 mayoral primary are likely to be unyoung, unpoor and Jewish. Jews should make up between 40 and 50 percent of the vote and the way they cast their ballots will probably determine who becomes the Democratic candidate for Mayor.

Like their unpoor and unyoung counterparts in Middle America, New York City Jews are losing their New Deal liberalism with alarming speed. Daniel P. Moynihan, professor of Education and Urban Politics, and Nathan Glazer, professor of Education and Social Structure, argue in Beyond the Melting Pot that a good deal of the growing conservatism of the city's Jewish population is a reaction against the increasing assertiveness of the black population.

Many felt that the beneficiary of this change would be volatile Bronx Congressman Mario Biaggi. However, the most decorated policeman in America locked horns in a tooth-and-nail battle with the baddest hombre of them all, the media, and came out looking like a rookie. For weeks, Biaggi kept insisting that he hadn't taken the Fifth Amendment in front of a grand jury. When the testimony was released and it showed that he had indeed taken not only the Fifth but entire Bill of Rights, his campaign machinery stopped functioning.

Following the maxim that when a guy is down you step on him. The New York Times immediately went to work on Biaggi. First they revealed that the Bronx District Attorney had uncovered some undisclosed "new evidence" in a shooting Biaggi committed 14 years ago when he was a policeman.

The day after publishing this story. The Times reported that Biaggi was to be called in front of yet another grand jury. Biaggi did not know how to handle these thrusts. While no one has ever uncovered any evidence of any wrongdoing by Biaggi, the Bronx Congressman's response to these charges only left people convinced something was fishy. Biaggi flew off the handle after each of these stories, charging that there was a conspiracy against him. He clarified nothing and with the release of the grand jury testimony only showed that he was a liar.

Imagine the problem now facing the scared Jewish Grandmother on the Grand Concourse! Most likely she and other moderate-to-conservative Jews will swing into the camp of 67-year-old Comptroller Abe Beame. While Beame's most visible attribute is his 5'2" height, he has the reputation of being a good fiscal manager. While Jews realize that Beame will not talk as tough as Biaggi does, they know that he will at least keep the city in the black.

The other two candidates, Herman Badillo and Al Blumenthal, will probably split the diminishing liberal Jewish vote. Blumenthal has the support of most liberal reform Democrats in Manhattan, but not much else. He has very poor name recognition and no money, so that he can't go on television. Badillo did well with liberal Jews four years ago, but this time lost the support of the reform umbrella group, the New Democratic Coalition. His only hope now is that The New York Times endorsement he recently received will give him a big boost with the liberals.

However, it seems unlikely that Blumenthal or Badillo can muster enough votes to get into a runoff primary. The big question is whether Biaggi has kept himself clean enough to remain the shabbas goy of the Jewish Grandmothers on the Grand Concourse.