Harvard police arrested six Cambridge teens Monday night, shortly after the youths allegedly held up a Harvard graduate student at knife-point in the lower Radcliffe Yard.

According to Harvard Police Lt. Charles Schwab, one of the teens approached the student and demanded his money at approximately 8:30 p.m.

When the graduate student refused and began to walk away, the juveniles and 17-year-old Cambridge resident Paulo Silva allegedly surrounded him and said, "Give us your money or we'll hit you."

The graduate student, whose name police refused to release, declined. One of the teens then threatened him with a six-inch, camouflage hunting knife and began to search his coat and pants pockets. The student gave the suspects $80, and they fled from the scene.

After the incident, the victim walked to the Harvard police station where he gave a detailed description of the teens.

Officer Kevin Bryant then identified the group walking near Oxford and Hammond Streets. Police found the graduate student's four $20 bills on one of the teens and the knife in nearby bushes, authorities said. Each teen was charged with assault and battery and armed robbery.

Officers Robert Kotowski, Jim McCarthy, Robert Sweetland and David Lee assisted in the arrest.

Silva, who will be tried as an adult, was taken to the Cambridge police department and arraigned yesterday at Cambridge District Court. A bail hearing is scheduled for Friday, according to the0 District Attorney's office.

The five juveniles were transferred to the Department of Youth Services, according to Nancy Danforth, a probation officer for Cambridge juvenile court