A federal magistrate yesterday sentenced two marines to a year's probation for a nighttime attack in July on two men on the grounds of the Iwo Jima Memorial in Arlington. Charges against a third marine were dismissed.

According to testimony, Philip R. Watts and Tyree A. Hilkert of Arlington were accosted about 11 p.m. on July 20 as they walked home from a convenience store. Hilkert ran for help after the marines allegedly knocked Watts to the ground, kicked him and threatened him with a knife.

The servicemen accused Watts and Hilkert of attempting to solicit homosexual favors, according to court documents. Watts escaped to a passing car, which was pursued by the trio who banged on the doors, the documents said.

A 10-minute chase ended when the car in which Watts was riding pulled up at a military police booth at the entrance to Fort Myer and the marines drove off, according to testimony.

Sentenced yesterday by U.S. Magistrate W. Harris Grimsley to one year's unsupervised probation and $100 fines each were Cpl. Cody C. Coffman and Cpl. Joseph D. Zuffelato. Both men pleaded guilty to assault charges at a hearing Aug. 6.

Grimsley dismissed an assault charge against Cpl. David O. Billingsley to which Billingsley had pleaded guilty last month. Lawyers familiar with the case said a pre-sentence report indicated Billingsley had not been involved in the physical assault on Watts.

The marines, all in their early 20s, were assigned as military policemen at Henderson Hall, the Marine Corps headquarters in Arlington, at the time.

There have been numerous assaults around the memorial in recent years. Some of the victims were acknowledged homosexuals who used the grounds as a meeting place. In October 1976, Ronald J. Pettine, a former campaign aide to Rep. Morris K. Udall (D-Ariz.), was bludgeoned to death by an assailant.