ARREST IN MURDER OF HUEY NEWTON

A man described by police as a drug dealer has admitted killing Huey P. Newton, the co-founder of the Black Panthers, the police said tonight.

The man, Tyrone Robinson, 25 years old, of Oakland, told the police he killed Dr. Newton in self-defense early Tuesday morning, Sgt. Dan Mercado said at a news conference at the Oakland Hall of Justice. Mr. Robinson, who is on parole for a robbery conviction, admitted to the killing early today and is scheduled for arraignment Tuesday.

Sergeant Mercado said Mr. Robinson ''considered the murder a means to advance'' in the Black Guerrilla Family, a narcotics distribution gang that operates in California's maximum-security prisons, including San Quentin, where Dr. Newton served time. 'He Figured We Already Knew'

''He wanted to be a high-mucky-muck,'' Sergeant Mercado said later in an interview. ''He was a foot soldier and he wanted to be a shot caller. He figured we already knew. We felt we had him and he knew it.''

He said that Dr. Newton and Mr. Robinson, who had known each other for two years, argued over a cocaine deal and that Mr. Robinson then shot the 47-year-old former leader of the Black Panthers.

Mr. Robinson contended that Dr. Newton pulled a gun when the two met at a street corner in the drug-torn neighborhood, Sergeant Mercado said, but investigators said they found no evidence Dr. Newton had been armed.

The killing occurred in a neighborhood where Dr. Newton, as minister of defense for the Black Panthers, once tried to set up social programs to help destitute blacks.

The police said Mr. Robinson told them he refused to sell Dr. Newton drugs and that the two argued for about a minute. Investigators believe that Dr. Newton stole drugs from the gang. Several Witnesses

Sergeant Mercado said a man accompanying Mr. Robinson witnessed the shooting. And the police said they had located several other witnesses who disputed Mr. Robinson's account of the killing. There have been no other arrests in the case, Sergeant Mercado said.

Mr. Robinson was arrested Tuesday for investigation of felony possession of a firearm about a block from the crime scene. He was questioned about Dr. Newton's murder, but was not considered a prime suspect until Thursday.

Two other men were arrested at the same time on weapons violations, but are not considered suspects in the case, Sergeant Mercado said.

Dr. Newton came to prominence in the late 1960's as co-founder and defense minister of the Black Panther Party, which advocated that ''blacks ought to defend themselves with arms when attacked by police,'' in his words, until a ''democratic socialist society free of racism'' could be achieved. He was convicted of manslaughter in 1968 for the killing of the Oakland policeman, but was later released after a successful appeal and two retrials.

He later fled to Cuba, returned, faced new charges in other crimes, served time in prison and finally earned a Ph.D. in social philosophy from the University of California at Santa Cruz in 1980. But in recent years he acknowledged abusing drugs and alcohol and served more time in prison for parole and drug violations. Funeral Arrangements

Dr. Newton's funeral will be held Monday at the Allen Temple, which can seat 1,200 people. The organizers say they expect an overflow crowd, and speakers will broadcast eulogies and sermons outside the temple. Members of Dr. Newton's family expect as many as 2,000 mourners from around the country to file past the open coffin.

''You can rest assured thousands of people will be standing outside,'' said the Rev. Cecil Williams, pastor of Glide Memorial Methodist Church in San Francisco. He is helping the family with funeral arrangements.

''Many of the big names of the 60's and 70's will be coming in,'' he added. Bobby Seale, another co-founder of the Black Panthers, will be among the speakers.

''People who knew Huey in the past and present need to express some things,'' said his sister-in-law, Barbarette Newton. She declined to name other mourners.

''A lot of these people will be needing security,'' she said. ''Black Panthers, people who supported them, primarily.''