The prosecution rested its corruption case against Prince George's County Sheriff Don Edward Ansell yesterday, with testimony from an accounting expert questioning the source of funds Ansell used to pay his children's private school tuition in September 1976.

The expert, Robert Milne, said he had reviewed the sheriff's finances and that he could find no evidence that the sheriff had withdrawn any money from his three bank accounts to generate the funds for a $2,160 cash tuition payment the sheriff's wife had made to the school. According to testimony, Ansell's wife made the tuition payment to the Clinton Christian School, which the three Ansell children attend, on Sept. 14, 1976.

The prosecution contends that money for the tuition came from $1,-920 that the sheriff pocketed from ticket sales to the "Deputy of the Year" banquet," which the sheriff's department sponsored on Sept. 10, 1976.

The 40-year-old sheriff is charged with putting that $1,920 to his personal use, then failing to report that income on his state income tax return and lying to a grand jury about it.

According to yesterday's testimony on September 13, 1976, the day before Ansell's wife made the tuition payment, one of the sheriff's secretaries had cashed $1,920 in checks at the Suburban Trust branch at Upper Marlboro, proceeds of ticket sales to the "Deputy of the Year" banquet.

The secretary, Joan Schult, testified that she was told to cash the checks by Maj. Guy Williams, who was second in command in the sheriff's department at the time and has been indicted along with Ansell in connection with the alleged banquet scheme.

Schult said she believes she gave the money from the checks to Williams. About half the checks were endorsed with the sheriff's own signature. Guy Williams had signed the sheriff's name on the back of the remaining checks.

Schult said she could recall no instance in which she gave any tic ket money to the sheriff or was asked by the sheriff to cash checks for the banquet.

In calling an expert accountant, Assistant State's Attorney Robert Bonsib attempted to show that the cash payment Mrs. Ansell had made in September, 1976, about the time of the banquet, broke the pattern of payments that the Ansells had made to the school in previous months when their tuition payments were all made by checks.

Milne, the accountant, testified that he could find no evidence that the sheriff made any withdrawals from his Police Federal Credit Union account or from his savings accounts at either the Bank of Brandywine or Suburban Trust Co. to generate the funds for the $2,160 cash tuition payment in September 1976.

It was the first time in the two years that the Ansells had been paying tuition to the school in which the accountant could not account for the source of funds for the payment, according to testimony.

Defense attorney Victor Houlon charged that the prosecution has been unable to "put 10 cents in the sheriff's hand," and said he will ask Judge George Bowling, who is presiding over the trial, to dismiss the case today.

Ansell elected to be tried by a judge, without a jury, and Bowling was brought in from Charles County to hear the much publicized case. The trial caps a six-month-long investigation in which the sheriff's financial records from January 1974, to November 1977, were subpoenaed, and hundreds of witnesses, many of them current or former employes of the sheriff's department, were interviewed.

At one point during the trial Houlon charged that prosecutors had tried to "rake up the most viligfying mud (they) could find" on the sheriff in investigating this case.

Under questioning by Houlon, the investigator for the state's attorney's office who had worked with Bonsib on the Ansell investigation acknowledged that he had gone to a motel in Upper Marlboro and asked employes if they had seen Ansell there with any women.