Two men surprised a security guard at the Rhode Island Statehouse early yesterday, made off with a silver collection and then demanded that a 2 1/2-month state prison lockup be ended in exchange for returning the silver.

An aide said Gov. J. Joseph Garrahy would ignore the robbers' demand.

"The governor's certainly not going to be intimidated by that type of foolishness," said Michael Ryan.

Officials were scouring state archives for records and photographs of the collection, made in 1907 for the U.S.S. Rhode Island and loaned to the state when the battleship was decommissioned in 1923. The original price was $7,000.

Adolph Giannini, the guard surprised and tied up by the intruders, was told the collection would be returned when Garrahy ordered an end to the lockup imposed at the Adult Correctional Institutions after an Aug. 26 inmate-guard brawl in which 10 correctional officers were injured.

Under the restrictions, about 400 maximum security inmates are allowed out of their cells for one hour a day.

Among the silver pieces missing fromt he shattered glass display case at the entrance to the Senate chamber were a large soup tureen, some serving platters, a sugar bowl and various other implements. It could not be determined immediately if the collection was insured.