A Montgomery County jury convicted Wheaton businessman Douglas L. Sanders last night in a murder-for-hire plot on the life of an Internal Revenue Service employe.

The Circuit Court jury, which heard four days of testimony, deliberated 5 1/2 hours before finding Douglas L. Sanders, 43, guilty of attempted murder and solicitation to commit murder. Sanders, the proprietor of two trucking firms in Montgomery and Prince George's counties, is free under $100,000 property bond; sentencing was scheduled for late February.

The prosecutor, Assistant State's Attorney Michael Mason, said he will seek a 25-year prison sentence without the chance of parole.

The prosecution argued that Sanders asked an acquaintance last March to kill IRS auditor W. Stewart Connard after Sanders was told by his accountant that his tax returns for the last nine years were under investigation.

The acquaintance, Robert Lee Smithson, was the prosecution's star witness. After being arrested on a shoplifting charge March 18, he told police of a scheme aimed at Connard and agreed to wear a concealed microphone while talking with Sanders.

In that recording, played for the jury, Sanders told Smithson he had "got lucky" and obtained a gun and bullets to kill Connard and instructed Smithson to locate the IRS employe.

Sanders' attorney, Louis Fireison, attacked the credibility of Smithson, who testified he spent 20 of his 38 years in jails and reformatories. Fireison also suggested that Smithson cooked up the murder plot story to get out of his arrest on charges of stealing steaks from supermarkets.

Several IRS agents testified that Sanders was not under investigation when time he allegedly began plotting, and the defense argued that Sanders therefore had no motive for the crime.

Sanders still faces trial on charges of illegal possession and improper use of a gun