District Mayor Marion Barry and Fairfax County Board Chairman John F. Herrity plan to sign an agreement Monday outlining procedures the two jurisdictions will follow in the event of disturbances or escapes at the Lorton Reformatory, the District-run prison in southern Fairfax County.

The two men met in January and Barry promised then to improve procedures for notifying Fairfax authorities.

Herrity and other county politicians sharply criticized District officials after several incidents at Lorton last winter. They charged that the city intentionally kept county officials in the dark after several disturbances and escapes, and called for tighter procedures.

Among the provisions in the new agreement:

*The D.C. Department of Corrections will notify county police within five minutes of a suspected or confirmed escape or failure to return from furlough.

* Lorton's siren will be sounded within five minutes of a confirmed escape to alert nearby county residents.

* If there is a riot or other disturbance, prison officials will notify county police immediately after notifying the D.C. Director of Corrections.*The city will reimburse Fairfax for use of the county's police helicopter when it is used to search for escapees.

The agreement also calls for regular meetings between top county police and city corrections officials, as well as joint training programs for officers from the two jurisdictions.

"This is by far the most comprehensive and complete agreement we have ever had," said Fairfax police spokesman Warren Carmichael.

The Lorton facility has long been a sore point between D.C. and Virginia officials, who want the prison closed and the prisoners moved into new or expanded facilities in the city. In the early 1970s, the county and the state attorney general sued the city, which agreed to limit the number of prisoners at Lorton and tighten security there.

The city runs six facilities, ranging from youth camps to a maximum security prison, on its 3,000-acre reservation at Lorton.