Police brutality charges brought by the father of a 16-year-old Fairfax County youth who witnesses said was beaten while being arrested at a Franconia roller rink in January were dismissed yesterday by Fairfax County Police Chief Col. Richard A. King.

King said he accepted the decision of a police trial board, which found that Officer Keith M. Florence did not use "excessive physical force" in the Jan. 6 arrest of Howard L. Cadle of 6707 Wakefield Dr. at the Franconia Roller Rink.

Florence is one of three county policemen from the Franconia district station who arrested Cadle on a Juvenile Court warrant for violating probation. Witnesses to the arrest, which took place in the back room of the rink, said they saw policeman hit Cadle, who was wearing roller skates, repeatedly on the head and shoulders with their billy clubs.

King said yesterday that "in the process of arresting Cadle, the officers resorted to force, which required that Cadle be given medical treatment." The youth was treated at Mount Vernon Hospital after the arrest for scalp cuts and multiple bruises on the shoulders and back.

Brutality charges against the other two arresting officers, Robert T. Hubbard and James F. Kelly Jr., were dismissed without a trial board hearing because of insufficient evidence, King said.

King did not release a police version of why Calde was injured during the arrest, and he refused comment on how the decision was made to drop charges against the officers. King said all findings of the police department's internal affairs section are not public information. He asked that the public "have a little faith" in the integrity of his police force.

Lacy Cadle, the father who filed the brutality charges, said yesterday he was "totally surprised" at the police findings. He said he was planning further action in the matter that will be "independent of what the police do." Cadle's attorney, Thomas H. Dameron, called yesterday's decision "extremely unfortunate."

In his announcement yesterday, King said he was breaking a precedent for the county police by publicizing internal affairs action. He said the announcement was made to "assure the public that we do an in-depth investigation."

Three of the five other major police departments in the Washington area make public the findings of police trial boards, which usually are three or four persons panels made up of police officers or citizens. Arlington, Prince George's County and the District of Columbia release trial board findings, police spokesmen said yesterday.

In Alexandria, trial board information is not released, and in Montgomery County releas is up to the chief of police.

King said yesterday he opposes the release of all trial board findings because of his feeling that internal affairs information "in general" should be kept secret.

King was asked about other recent allegations of police brutality stemming from a melee at a Rte. 1 night club on March 18. Several patrons of the One South Restaurant Night Club have filed brutality complaints, claiming that police went on a rampage in the club, striking and arresting patrons who were doing nothing illegal. King said he could not comment on the matter because it was under investigation.

"It is a sign of the times," King said, that complaints about brutality are made "that may or may not have foundation." He said also the police department screens its employes carefully, "We don't have any sadist on the department," he said.

The trial board that found Florence did not use excessive force arresting Cadle was made up of a police captain, two lieutenants and two officers of Florence's own rank.

Because of a new law passed this year by the Virginia legislature, the so-called "policeman's bill of rights," the make up of trial boards after July 1 will be changed. The police department will choose one member, the defendant will choose another and the third member will be chosen by the first two.

The law applies to all police departments in the state with 10 or more members.