Melvin Waters Jr., a ninth grader who was barred from John Hanson Junior High School for bringing a weapon to school, was formally expelled last week under a tough new Prince George's County discipline policy, his father said.

Melvin Waters Sr. and the youngster's stepmother, Karen Waters, have challenged the use of the policy mandating expulsion for weapons possession without regard to the circumstances or prior background by appealing the decision to the school board. The 14-year-old said he brought the weapon--a martial arts device consisting of two lengths of dowels connected by a chain--to school last month to protect himself. No blows were struck with the weapon during a brief fight between Waters and some other students, school officials said.

As required by a school board policy passed last August, John Hanson principal John Flynn recommended Waters' expulsion last month. Three weeks ago, charges were heard in a conference between Flynn, school disciplinary officials, Waters' parents and Clark A. Estep, executive assistant to School Superintendent Edward J. Feeney. Estep's letter of expulsion arrived at the Waters home last week.

"I anticipated their response," said Melvin Waters Sr., "so I sent out the request for appeal on the day their letter arrived." The appeal is set for Feb. 17, Waters said.

The expulsion is permanent, unless the school board reverses it on appeal. More than 60 students have been expelled under the new policy this year. Only one out of 10 appeals heard by the school board has been granted this school year, officials said.