NEW YORK, JULY 12 -- A federal judge declared a mistrial today on 26 felony counts against John A. Mulheren Jr., the flamboyant trader already convicted of illegal dealings with inside trader Ivan F. Boesky.

U.S. District Judge Miriam Goldman Cedarbaum dismissed the jurors, who on Tuesday found Mulheren guilty of four counts of conspiracy and stock manipulation.

"I am now persuaded that unanimity is beyond the reach of this jury on the remaining counts," Cedarbaum said late in the panel's ninth day of deliberations.

Mulheren, 41, was an aggressive and successful trader of stocks of companies targeted for takeover before he was implicated in 1988 in the government's fraud investigation by Boesky, a former friend and associate.

His trial in federal court in Manhattan was marked by Boesky's first public testimony under his settlement with investigators. Boesky spent two years in prison and paid $100 million in penalties to settle insider trading charges.

Mulheren joked with supporters after the mistrial, reflecting a casual demeanor that was his trademark on Wall Street and in court. Mulheren has said he went to trial, unlike others implicated in wrongdoing, as a matter of principle.

"Lots of money spent and no answer given," he said.

Prosecutors said they could not immediately comment on whether they planned to retry Mulheren on the outstanding counts of securities fraud, mail fraud and record-keeping violations. "We're very satisfied with the verdict," Assistant U.S. Attorney Scott Gilbert said.

Cedarbaum scheduled an Oct. 5 sentencing for the four counts on which Mulheren was convicted. He faces up to five years in prison and a $250,000 fine on each count.

Defense attorney Thomas Puccio said he planned to appeal the convictions. "It's been my view that Mr. Mulheren is not guilty of any of the charges," he said.

The charges that were not decided by the jury alleged that Mulheren secretly held large blocks of stock to help Boesky evade taxes and federal securities disclosure laws.

Mulheren was convicted of helping Boesky drive up the price of Gulf & Western Inc. stock in 1985. That outcome marked the first trial conviction based on court testimony by Boesky, who agreed in 1986 to cooperate with prosecutors in settling the biggest case of illegal insider trading ever.

Co-defendant Leonard DeStefano, 34, a former trader at Mulheren's defunct firm Jamie Securities, was acquitted of all conspiracy and record-keeping charges.