A former employe of the Red Lobster Inn Restaurant in Alexandria pleaded guilty yesterday to charges of robbery and the serious wounding of three restaurant employes during a hold-up of the establishment last Dec. 18.

In return for the guilty pleas, the prosecution dropped two other charges - burglary and attempted malicious wounding - against Charles Preston Sanders, 28, of 4828 Kenmore Ave. in Alexandria. The five charges to which Sanders pleaded guilty carry a combined minimum penalty of 21 years in jail, although the judge could suspend part of that term.

Assistant Commonwealth's Attorney Thomas Rawles Jones Jr. said a second man, Roger Alan Turner, 25, of Woodbridge, who is charged with armed robbery in the case, was ready to testify against Saunders. Turner is scheduled to go on trial March 23 in the robbery.

In a statement read before Alexandria Circuit Judge Wiley R. Wright, Jones said Sanders, a cook at the restaurant at 555 S. Van Dorn St., let Turner in through the back door as the establishment was closing for the night. Turner hid in the women's restroom, Jones said, and loaded a shotgun as Sanders left through the front door.

Later, the prosecutor said, Sanders reentered after forcing the door open and both men forced the associate manager, Michael McCool, 23, into an office, demanding the day's cash receipts.

After McCool turned over two cash boxes containing $1,200, Jones said Sanders ordered the four employes into a walk-in freezer.

The two men shut the freezer door, Jones said, but Sanders was afraid he had been recognized by his coworkers even though he had pulled a knit cap and turtle-neck sweater over hsi face. Sanders then opened the door and fired four shotgun blasts into the freezer, seriously injuring three of the four employes, Jones said.

Another restaurant employe, unaware of the events inside the restaurant , and who had asked Sanders for a ride home, according to Jones. That employe later saw Sanders throw the shotgun into the Potomac River and discard two cash boxes in the western part of Alexandria, Jones said.

Jones said that employe led police to two sites where evidence was recovered.

Sanders is scheduled to be sentenced April 11.