WELL, JOSEPH CRUZ is no longer living on a traffic island in the middle of New York's East River Drive. He has been taken to Bellevue.

And columnist Jimmy Breslin has moved into his old place.

And city authorities are pulling out their hair.

Breslin says he is staying until Cruz, a 55-year-old World War II veteran who was thrown out of his hotel room for nonpayment of rent, is released. The writer has settled in with beach umbrella, bathing suit, radio and some light summer reading.

"I sat in the sun, digging my toes into the sand," he wrote in his column for the New York Daily News, "and now and then looked up through the leaves of the young maple trees across the street and followed a tramway car as it slid through the sky on the way back from Roosevelt Island.

"I found my beach so thoroughly delightful that I remained for quite some time, and I intend to be there with my book and umbrella, waving at motorists, until Joseph Cruz is freed."

The sand comes from 20 traffic barrier drums that city workers put on the island to discourage other tenants. Obviously, the workers had never dealt with the likes of Breslin, who helped get a court order Sunday requiring the hospital to explain exactly what it means by keeping Cruz in a mental ward for "the crime of attempting to live decently while being poor."

Reached by telephone last night, Breslin said that he had gone to bat for Cruz because "they lifted the guy without due process, and that's a very important principle. There's a phrase, habeas corpus, 'produce the body.' You are not allowed to take a person and incarcerate him without a hearing. But they just threw him in because he was an embarrassment."

But when an attorney sought Cruz's release at a three-hour hearing yesterday, State Supreme Court Justice Donald Sullivan ruled that Cruz may be mentally ill and ordered him kept in Bellevue for psychiatric testing. He said the test results should be reported to him Friday.

Nevertheless, said Breslin, "The question of the homeless is going to become a major topic and a test of us as a people. What kind of a people are we if we have this? The answer is, we've lost the ability to assist, we've replaced it with a new standard, and the standard is greed.

"It's above and beyond this one guy," he said. "The traditional answer of the rich when they see vagrants is, the man must be mad, and they look to psycho them. They always say the man on the street corner is mad.

"The rich are uncomfortable at the sight of anyone homeless. The mayor has to pass there every night on his way to Gracie Mansion. They had the greatest show of bureaucracy trying to move one f------ guy because he was an embarrassment. They drove the man nuts."

As for Cruz's erstwhile home on East River Drive, Breslin said, "It's a delightful place. I love the place." However, he was located last night at a getaway he knew of long before he discovered the delights of the traffic island: Costello's bar, on 44th Street.

Jimmy Breslin, you recall, is a larger-than-life figure who makes New York the setting for his life movie and its inhabitants the bit players. When Norman Mailer ran for mayor, Jimmy Breslin ran for the No. 2 spot, president of the city council. When Son of Sam wanted to talk, who would he talk to but Jimmy Breslin? As for his latest campaign, Breslin cautioned, "Don't call it a crusade. Someone always gets killed in a crusade."

Two years ago, when Cruz was evicted, he said it was because his Veterans Administration check came late, Breslin wrote. Cruz refused to move into a city shelter for the homeless, which he says are dangerous and filthy, and took to the streets.

Early this summer he found just the spot, a traffic island at the 61st Street exit of FDR Drive, also known as East River Drive, southbound. A low wall separates the triangle from northbound traffic. The other side faces southbound traffic, much gentler and quieter, as it is making the turnoff onto 61st. Cruz installed his furniture: a bed, a chair, a cooler, a Charlie Brown wastebasket, a painting of ballerinas and his jerry-built stove.

And there he lived a smoggy idyll, dashing across to a Parks Department building to bathe and wash his clothes. With an overpass for a roof and an endless river of speeding cars for neighbors, he would smile at the commuters, raise his beer to toast them as they passed, and bring a little brightness into a lot of gray lives. Now and then a driver would stop and donate a dollar or two or maybe a six-pack.

It was a lovely way to spend a summer day. In the evenings, when the commuters were gone and the moon came up, he could watch the light glinting on the black waters of the East River. There was so much to see that a man could hardly concentrate on his book. There he was, a beacon of quiet in a storm of steel.

Unfortunately, Breslin charged, one of the commuters was Mayor Ed Koch, who didn't like the whole idea. City agencies moved into the case.

"Why are they bothering me now?" Cruz said. "I've been living on the streets for over two years and nobody cared."

Last Friday a Human Resources Administration psychiatrist showed up with Cruz's daughter Evelyn. Sensing trouble, Cruz scrambled out of his chair and darted across the highway.

As Breslin put it, "He suddenly gave the bureaucracy all that it needed. Mr. Cruz is a danger to himself and others, the psychiatrist ruled."

The fact that he had been there all summer, harming no one, carried no weight, apparently. Six policemen took him away and removed his furniture. He offered no resistance.

Said Breslin: "They came up with suicide at the 11th hour . . . Because of the seriousness of the charges, we have to meet them with an equal degree of seriousness." He promised to get "the top guys, the best available," to testify on Cruz's behalf.

And for the rest of Breslin's stay on the traffic island, he will not be limited to the "delightful" sights and smells of East River Drive. This morning, the London Daily Mail was sending him a hamper from Fortnum & Mason, where the British upper class has always bought its best gourmet foods. In the hamper: duck, champagne, pate' and caviar.

The hamper was to be sent by Concorde, lest it spoil.