Almost half of the 253 complaints filed against Fairfax County Police officers last year were justified, according to a summary of an internal police study released yesterday by the head of the 648-member force.

Only one of the valid complaints involved use of excessive physical force, according to Police Chief Col. Richard A. King. Another officer was dismissed on charges of stealing funds from a police station fund and two were disciplined for unwarranted use of their pistols, King said.

The force is currently being investigated by a federal grand jury in Alexandria because of an incident in which a 16-year-old youth claimed he was beaten by three officers who arrested him on charges of violating his parole. Also under investigation by the grand jury is the county's internal police review board, an all-officer agency that reviews charges against the Fairfax officers.

King yesterday called the percentage of justified complaints "normal," citing 238 complaints the department had recorded in 1976."There are in-excess of 250,000 contacts (by policemen) with the public every year," he said. "That's (253 complaints) not too bad."

Most of the complaints involving the officers were filed by their superiors and involved dress, conduct and disobedience of internal regulations, King said.

In addition to the dismissal of the officer accused of taking money from the police station, King said three other officers under investigation resigned from the force last year. However, the chief said yesterday he could not remember details of those incidents.

"I have nothing to hide," King said. "That's the reason for the report."

The excessive force charge stemmen from an incident involving three officers and a "small group" of people, King said. One of the officers "roughly handcuffed and put a suspect into a squad car," King said. "The incident involved the use of a foot." King said he could not remember other details of the incident. The charge resulted in th unnamed officer's suspension from the force for 10 days without pay, King said.

The unwarranted firing of guns charges resulted in a loss of two days off for each officer involved, but no suspension or loss of pay, King said. Both were cases of officers firing warning shots, an action not allowed by the department, King said.

"We do react to complaints. We do react in a positive manner," King said. "Obviously, not all complaints are valid," he said.

The study showed that, besides the 117 valid complaints, 27 other complaints could not be proved or disproved, 70 were found to be accurate but proper and lawful under the circumstances and 65 were found to be false, King said.

"We do get complaints, onsviously," King said. "But we don't get a high number." Over the years, he added, "there has been some lessening in the number of complaints about excessive use of physical force."

Of the 283 officers against whom complaints were filed last year, 44 had received prior complaints during 1976. Complaints against only three of these repeaters, however, were found to be valid by the study.

King said he has not yet compiled statistics on the number of complaints against the force for 1978, the period involved in the grand jury investigation.