BRIGHT PROMISE AND DARK DECLINE: PORTRAIT OF COUPLE IN CHILD MURDER CASE; Joel Barnet Steinberg

BRIGHT PROMISE AND DARK DECLINE: PORTRAIT OF COUPLE IN CHILD MURDER CASE; Joel Barnet Steinberg

By KIRK JOHNSON

LEAD: The portrait of Joel Barnet Steinberg, who has been charged with the beating death of his 6-year-old adopted daughter in their Greenwich Village town house, is an incomplete image of an intense and complex man who closely shielded his inner life.

The portrait of Joel Barnet Steinberg, who has been charged with the beating death of his 6-year-old adopted daughter in their Greenwich Village town house, is an incomplete image of an intense and complex man who closely shielded his inner life.

At times, some say, he could be warm and fatherly and generous. But, many others say, he was more often reclusive and manipulative and sometimes abusive to those close to him, a man who in 17 years as a defense lawyer in New York City showed a remarkable aptitude for losing friends.

Ultimately, Mr. Steinberg was unknowable, many of his acquaintances say. But prosecutors investigating the child's death say a truer picture of the 46-year-old attorney is emerging, that behind the doors of his apartment at 14 West 10th Street existed a world of drugs, filth and violence.

The murder case went before a Manhattan grand jury yesterday but a police task force continued to look beyond the death and into allegations that Mr. Steinberg was involved in drug dealing and illegal adoptions. The Manhattan District Attorney, Robert M. Morgenthau, said Mr. Steinberg, ''may yet be charged with other crimes.''

''There are very many unanswered questions - so many stories to sort out,'' said another senior law-enforcement official who is participating in the investigations. ''I'm not sure when we'll know all the answers.'' 'Pushy and Reclusive'

Mr. Steinberg, a burly, bushy-haired man who grew up in the Bronx and Westchester County and who has lived in the Village since the late 1960's, is charged with the murder and assault of his adopted daughter, Elizabeth. The girl, whose adoption shortly after birth on Long Island is also being investigated, was declared dead from brain injuries Wednesday after being taken by paramedics from the 10th Street apartment early Monday morning.

The woman who has lived with Mr. Steinberg for 17 years, Hedda Nussbaum, 45, has been charged with the same crimes. She remains hospitalized with injuries that prosecutors say were also inflicted by Mr. Steinberg.

Mr. Steinberg, through his attorney, Robert I. Kalina, has denied all the charges, as has Ms. Nussbaum, but neither defendant has made any statements to the police. Mr. Kalina did not return repeated telephone calls from a reporter.

In interviews with more than a dozen former associates and law school classmates, however, Mr. Steinberg was repeatedly described as complex, private and, to a large extent, unknowable. One lawyer who said he knew Mr. Steinberg in the 1970's, but who refused to be identified, described Mr. Steinberg as ''both pushy and reclusive.''

Others said he was a thoughtful and philosophical man, a ''bohemian.'' Disputes With Associates

''I'm not sure you could be friends with him, ultimately,'' said Brian C. Baker, who shared a law office with Mr. Steinberg in the early 1970's and who parted less than amicably after six months.

''The word manipulative comes up most in my mind,'' Mr. Baker added. ''He could manipulate a banana out of a gorilla's hands and make the gorilla think he'd gotten a prize.''

According to civil court records and other lawyers, Mr. Steinberg commonly had problems with associates. Twice he sued and was countersued in the 1970's over office space in cases that involved disputes over such things as unpaid rent and improperly removed law books. At least three times he moved from one office to another in the 1970's, before beginning to work out of his 10th Street apartment in the early 1980's.

According to the charges against him, Mr. Steinberg had bruises on his hands at the time of his arrest. Investigators also found bloodstains on clothing and sheets found in the third-floor apartment and on a metal exercise bar found in the master bedroom.

Although few of the more than a dozen former associates interviewed said they admired Mr. Steinberg, only one said she ever saw any indication of abuse. 'Very, Very Nasty'

That incident occurred in the summer of 1972 aboard a small sailboat that Mr. Steinberg then kept off Long Island Sound. ''It was very unpleasant,'' said the attorney, who requested anonymity and said she was a law student at the time.

''He was very, very nasty, verbally abusive to a woman I assumed was his wife,'' she said. ''I remember it because I've so rarely been in a situation where I so badly wanted to leave but couldn't - it was very unpleasant.''

The attorney said she did not recall whether the woman on the boat was Ms. Nussbaum.

''I think everybody who knew him is shocked,'' said Ronald Kliegerman, a lawyer who has known Mr. Steinberg professionally for 15 years and last saw him about six months ago. Mr. Kliegerman said that many in the legal community are stunned that a lawyer would be accused of such crimes. Withdrew From School

An only child, Mr. Steinberg graduated from Fordham University in 1962 with a degree in political science and entered the New York University law school that same year. Two years later, in spring 1964, he withdrew from school, according to law school officials.

For the next year, until he began military service in the United States Air Force in April 1965, his actions and whereabouts could not be determined. Air Force officials said Mr. Steinberg was discharged as a first lieutenant in March 1968. He re-entered law school that summer and graduated in the spring of 1970.

As an attorney, Mr. Steinberg concentrated in the 1970's on criminal law - primarily drug cases, according to prosecutors and other defense lawyers - but also took many cases in family court, some involving adoption.

However, court officials and other attorneys agree that Mr. Steinberg's court appearances sharply declined in recent years. According to figures from the Assigned Counsel Plan for Manhattan and the Bronx, which supplies attorneys paid by the state for poor defendants in criminal and Family Court cases, Steinberg volunteered for 10 or more cases each year in the late 1970's. In 1980, the number suddenly increased to 36 - 20 involving criminal charges and 16 in family court. The following year, the number dropped abruptly to a total of seven cases. In 1982, only one case, and nothing since.

Investigators said they also believe Mr. Steinberg may have begun using drugs heavily at about that time, but because of the secrecy of grand jury proceedings, they declined to provide specific details.