James J. Carvino, 53, chief of the U.S. Capitol Police since 1984, resigned yesterday, according to officials. No reason for the resignation could be learned and Carvino could not be reached for comment last night.

"He just tendered his resignation," said Henry K. Giugni, sergeant at arms of the Senate and one of the three members of the Capitol Police Board, which supervises the 1,135-member force.

Harry B. Grevey, currently deputy chief for field operations, is to become acting chief of the force, which patrols a 40-block area that includes the Capitol. Its responsibilities include taking precautions against possible terrorist attacks.

Last year, in a move intended to promote flexibility and enhance the ability of the force to respond to possible threats, many longtime officers who had become familiar to members of Congress were shifted into new posts. The move created controversy and was rescinded after congressional protest.

About that time, many members of the force, citing low pay, high turnover and sagging morale, began a campaign to obtain union representation.

Carvino, a Brooklyn native and holder of a master's degree in administration, spent 22 years in the New York City Police Department. He retired with the rank of captain, and came here after seven years as chief of police in Racine, Wis.