NEW YORK (AP) _ A former mutual fund manager was convicted Tuesday of accepting a bribe in return for purchasing Drexel Burnham Lambert Inc. junk bonds on behalf of her clients.

The conviction of Patricia Ostrander came despite the testimony last week of former Drexel junk bond king Michael Milken, who denied offering any bribes. The verdict could be a blow to Milken's attempt to have his prison term reduced.

Milken, serving a 10-year sentence for securities-related crimes, testified under court order as a defense witness for Ostrander, a former top portfolio manager at Boston-based Fidelity Investments, the country's biggest mutual fund operator.

The government has maintained Milken set up lucrative equity partnerships to reward portfolio managers for purchasing Drexel junk bonds on behalf of their clients. The Ostrander case was the first jury test of that claim.

Ostrander remained free on a personal bond pending sentencing Oct. 5 before U.S. District Judge Richard Owen. She faces up to five years in prison on each of two bribery counts and up to three years for violating securities reporting laws.

Defense attorney Harry Manion said he would appeal the verdict.

The U.S. Attorney's Office was expected to send a letter to Milken's sentencing judge, Kimba Wood, describing Milken's testimony and the outcome of the Ostrander case, possibly as early as tomorrow.

Wood is considering Milken's request for a sentence reduction. Prosecutors had asked the judge to delay her ruling ''to avoid any prejudicial publicity'' during the Ostrander trial. Milken has served about 17 months in prison. Without a reduction, he would not be eligible for parole until 1994.

Milken is seeking the reduction in return for cooperating with the government. He testified for prosecutors in May in the case of Alan Rosenthal, a close friend and former Drexel colleague who was convicted of giving a kickback to a favored Milken client.

Prosecutors had praised Milken's assistance in that case. But a government official, speaking on condition of anonymity, said the Ostrander case contradicted Milken's assertion he did not illegally offer the money manager a stake in a Drexel investment partnership known as MacPherson Partners in 1985.

The charges against Ostrander stemmed from a $13,200 investment she made in a MacPherson. Prosecutors said the investment - which reaped Ostrander $750,000 - was meant to reward her personally for doing business with Drexel.

She denied the investment was a payback, saying she had no guarantee the investment would make a profit.

At a hearing before Milken's sentencing in 1990, Judge Wood found the government had failed to prove Milken committed any wrongdoing involving MacPherson, which consisted of equity in the Drexel-managed buyout of Storer Communications Inc.

The government asserted that Milken had misapproriated the equity stake in Storer to reward money managers for buying Storer junk bonds.

''Here Milken acknowledged his involvement, although he denied any corrupt intent,'' the government official said. ''The jury certainly found that there was corrupt intent.''

Assistant U.S. Attorney Kenneth Vianale declined to comment on the verdict.

Manion said he did not regret calling Milken to the stand, although it was unclear what the jury thought of his testimony. ''If it helped, it didn't help enough,'' he said.