Robert J. diGrazia, fired as Montgomery County's police chief Thursday, plans to contest his dismissal arguing it was unjust punishment for implementing reforms in the police department and speaking out on police issues, his attorney said last night.

DiGrazia intends to sue on grounds that the man who fired him, Charles W. Gilchrist, the new county executive, violated the "policemen's bill of rights," which is part of Maryland law and protects officers from arbitrary disciplinary punishment, according to Peter Davis, diGrazzia's attorney.

In firing diGrazia, Gilchrist said Thursday the chief "was no longer effective," in part because of his persistent disparaging remarks about police officers. DiGrazia, 50, was placed on administrative leave, continuing to receive his $52,811-a-year salary until he "can straighten out his affairs," Gilchrist said. Maj. Donald E. Brooks, 52, who diGrazia once tried to fire, was named acting chief.

In a lengthy prepared statement issued by his attorney, diGrazia said last night that when he tried to bring "professional programs and management reforms to an outwardly polite but inwardly stagnant department," he met with resistance from the "good old boys" presently or formerly in the department.

"I was fired for implementing these programs and speaking out on these issues and demanding the best for Montgomery County citizens," diGrazia declared. He added that he spoke openly about police issues to the dissatisfaction of the new county executive.

The action that apparently triggered diGrazia's firing was a statement the chief made at a public forum three weeks ago that most police officers "see the community as the enemy." DiGrazia maintained that his comment referred to a universal police problem and was no "indictment of the Montgomery police."

Attorney Davis said that in addition to citing the "policemen's bill of rights," he will argue that diGrazia is protected by the county charter, which states that any agency head appointed before Dec. 2, 1976, is a merit employe and therefore cannot be fired except for misconduct in office. He said diGrazia was appointed chief Nov. 15, 1976.

DiGrazia decided to go to court, Davis said, after the county executive and county attorney's office "refused to acknowledge the existence" of any rights the chief might have as a merit employe or under the officers "bill of rights."

Davis said he intends to either ask the Circuit Court for an order that would require Gilchrist to show why diGrazia would not be covered by the "bill of rights" or the merit system. Or, he said, he may seek a judgment as to whether the "bill of rights" and the county charter, which the merit system is a part of, would apply to diGrazia's case.

Gilchrist said Paul A. McGuckian, the man he chose to be the new county attorney, was one of the advisers who helped him conclude that diGrazia would have no legal grounds for an appeal if fired.

Assistant County Attorney Richard E. Frederick said the officers' "bill of rights" is meant to protect the rights of police accused of such things as malfeasance, drunkenness or corruption and would not cover the firing of a chief.

He said the county charter "clearly expresses" that department heads "serve at the pleasure of the county executive."

If it is determined that the "policemen's bill of rights" applies in diGrazia's case, he would be entitled to a trail before a police hearing board made up of a least three police officers. One would have to be of equal rank to the chief. Since normally the county chief would appoint the board's members, questions arise as to who would make the appointments and whether it would be fair if they were from the Montgomery County force, according to Allen Katz, attorney for the local Fraternal Order of Police.