Acting on a tip from a Conant Hall resident. Harvard Police early last Sunday morning arrested two 19-year-old Cambridge men who were cutting cocaine on a mirror in the lobby of a Law School dorm located on the corner of Oxford and Everett Streets.

James H. Graham of 5 Roosevelt Towers and John J. Trainor of 196 Sherman St. were charged with possession of a Class B substance, a felony. Police did not specify how much cocaine was involved.

Deputy Chief Jack W. Morse said yesterday police believed the men were trying to sell the cocaine to anyone who would buy it. Among other crimes reported to the Harvard Police during the week ending this past Thursday:

*Unidentified thieves last Friday, March 1, stole a Sony video recorder and a Technics tape deck, valued at $1500, which had been left unattended in the Science Center.

*Vandals smashed three windows at Eliot House early last Sunday morning. A screen was broken and a window smashed on the second floor of O-entry. A window was broken on the first floor of O-entry, and also in the back of the residence of Eliot Master Alan Heimert. Police had no estimate of the total damage.

*A pair of pants, a wallet, a watch, and a chain were stolen from a locker in the basement of the Indoor Athletic Building between 8 and 8:15 p.m. on Thursday. Total value of the items is $471.

*Four seat cushions valued at $180 were taken from a Thayer dorm room between 12 a.m. and 10 a.m. last Tuesday. The cushions were stolen while the owner was asleep in the room.

*A $435 tan camel hair coat was stolen from a coat rack in the men's locker room at Hemenway Gym last Tuesday.