The tampering charge said that on April 9 and 10, 1985, Sipp tried to ensure that a state witness, Walter Johnson, also of Springfield, would be absent from the insurance-fraud trial.
As his attorney entered the guilty plea, Sipp stood motionless in front of Judge Cornelius P. Sullivan. Sipp gave one-word answers until the judge described the witness-tampering.
Speaking in an even tone, Sipp said that he had not contacted Johnson but that he had spoken with Johnson's attorney.
Sipp offered to send Johnson on a vacation in exchange for the man's absence from the trial, according the county Assistant Prosecutor Gregg A. Shivers. Johnson's attorney informed the prosecutor's office of the offer, Shivers said, and the county tape-recorded a conversation between Sipp and the attorney.
Johnson was expected to testify that he had helped Sipp apply for the insurance policies, Shivers said. No charges were pending against Johnson.
"The goal of the investigation has been met by this plea," Shivers said. ''We have significantly deterred him from similar violations."
In 1981, Sipp was the nation's second-most-successful horse trainer. That year, horses trained by Sipp won 272 races at race tracks that included Keystone and Atlantic City.
On Dec. 18, 1984, a Burlington County grand jury indicted Sipp on charges of submitting $142,500 in inflated insurance claims on nine horses that died while in his care from 1980 to 1984.
Sipp's license to train thoroughbred racehorses has been suspended pending the outcome of the indictments. Charles Bradley, deputy director of the New Jersey Racing Commission, said the commission would look into the possibility of permanently banning Sipp from racing in the United States.
In a news release, county Prosecutor Stephen G. Raymond said he would inform the commission of Sipp's guilty plea and request that he be removed
Shivers said the prosecutor's office would have easily proven the insurance fraud charges against Sipp. "However, there would have been issues that would have taken time to explain to the jury," he said, adding that the evidence of witness-tampering would have been admissible at a fraud trial.
First Assistant Prosecutor Michael E. Riley said a fraud trial, which had been scheduled for Sept. 8, would have been expensive. Witnesses were to be brought in from England, California, Montana, Florida, Kentucky and New England, he said. Some of the witnesses had been present when Sipp purchased the horses, Riley said.
"It would probably have been the most expensive case to try in the last couple of years," Riley said. The county would have had to pay for witnesses' transportation and lodging during the trial, according to Riley, who estimated that the trial would have lasted four to six weeks.
The deaths of the horses still are the subject of civil litigation, Riley said.
Sipp's indictments and eventual plea resulted from a three-year investigation by the state police and the county prosecutor's office. Sentencing was scheduled for 2 p.m. July 25.
The prosecutor's office will not make any sentencing recommendation, according to Shivers, who said Sipp probably would face a maximum of five years in prison.