Prince George's County police and local FBI agents said yesterday they are trying to identify a woman who robbed three and possibly four Maryland banks in the last three weeks and copied another woman robber in Fairfax County last month who claimed to be carrying a grenade in a sock.

An FBI spokesman said they will review bank photographs today to determine whether the holdup of the Citizens Bank and Trust Co. branch in Prince George's Plaza about 8 o'clock last night was apparently committed by the woman believed responsible for the other three.

A Laurel woman was arrested about three weeks ago and charged with the October robberies in Northern Virginia. FBI officials said that reports of the first "grenade lady" prompted this newest copy cat.

Law enforcement officials said bank photographs from the first three Maryland holdups show the same unidentified woman. She does not match the descriptions of the robber in the Virginia crimes.

According to FBI agent Richard Weaver, the heavy-set woman with glasses got away with undisclosed amounts of cash in each robbery. County police said the woman, who wears a hat or scarf, walks up to a teller and presents a note saying, "This is a holdup, I have explosives." In one photograph, she is seen holding up what looks like a sock.

The first holdup on Oct. 23 was at the same Citizen's Bank and Trust branch at Prince George's Plaza that was robbed last night; the second was Nov. 1 at Suburban Bank at 5214 Baltimore Blvd., Hyattsville, and the third, Nov. 8 at 3716 Rhode Island Ave., Mount Rainier.

Prince George's police are offering a $1,000 reward for information in these cases. Calls are being taken through the confidential Crime Solvers line at 735-1111.