A District man who was found guilty earlier this week of a Christmas robbery at a church pleaded guilty yesterday to armed robberies at three other Prince George's County churches.

Gregory Williams, 30, of Edgewood St. NW, was found guilty Tuesday by a jury in Upper Marlboro of a robbery at the First Wesleyan Church of Oxon Hill, last Dec. 27.

Assistant State's Attorney Michael Whelan told the court that Williams took a shoebox used for contributions for missionary work and walked into the church as a Bible study group was meeting. He held a gun to one woman's head, Whelan said, and ordered the congregation to file up and drop money in the box.

At one point, Whelan said, the pastor handed Williams a Bible. Williams at first refused it, but then added the Bible to about $400 he had collected from the congregation.

Yesterday Williams pleaded guilty before Circuit Court Judge Audrey E. Melbourne to five other armed robberies, including these churches:

* Shiloh Church of God in Hyattsville, last Dec. 26. Prosecutors said that Williams had entered the church, said that he wanted counseling, and was directed to an office where the pastor, Samuel Carson, and an assistant, were counting the offering. Williams made off with about $300, prosecutors said.

* United Methodist Church of the Redeemer in Temple Hills. Prosecutors said that on Nov. 19 of last year, Williams went into the church office and demanded money from the pastor, Richard Nowers. Williams took $3 from Nowers, then ordered him to where the choir was practicing. Williams held the choir at gunpoint and took several hundred dollars, prosecutors said.

* St. Luke's Episcopal Church in Bladensburg. Prosecutors said that Williams went to the basement of the church last Feb. 23, where an Alcoholics Anonymous meeting was in progress, drew a pistol, and took between $300 and $400.

In addition, prosecutors said, Williams pleaded guilty yesterday to an armed robbery that netted $864 at the Aeor-Leasing Corp. in Mount Rainier in October 1981 and an armed robbery of the Goodyear Tire and Rubber Co. in Bladensburg last March 3, where he pulled a pistol on the manager and took $387 from the cash register.

Williams, who is being held in the county detention center in Upper Marlboro, is scheduled to be sentenced by Judge Melbourne on Feb. 3.