Violence on network television increased in 1976 and reached its highest level in almost 10 years, according to a study released yesterday by researchers at the University of Pennsylvania's Annenberg School of Communications.

While depicted killings "declined slightly" last year, the so-called "Violence Profile" found that the number of violent incidents on TV rose from 8.1 per hour in 1975 to 9.5 per hour in 1976. The amount of "violent action" measured rose "to the highest point on record," the survey said.

Release of the study was timed to preface hearings on sex and violence in television to be held Wednesday by the House Subcommittee on Communications. Dr. George Gerbner, dean of the Annenberg School and one of those who developed the profile, will be among those testifying during the day-long session.

The presidents of ABC, CBS and NBC - Frederick S. Pierce, John A. Schneider and Robert T. Howard - will also face questioning at the hearings, which are being held as pressure groups step up efforts to reduce television violence.

Gerbner will present his findings to the committee. The study found that the level of violence increased most during the Family Hour period instituted by the networks in alliance with the National Association of Broadcasting (NAB) and subsequently struck down as unconstitutional by a U.S. District Court in Los Angeles.

NBC was found to be the most violent network, with ABC second and CBS third. These rankings were the same in the 1975 profile and also correspond to the result of a separate TV monitoring project conducted by the National Citizens Committee for Broadcasting (NCCB), a Washington-based group currently in the forefront of the antiviolence campaign. An NCCB spokesman will testify at Wednesday's hearing.

The study also found that women, children and nonwhites were the character types most likely to be the victims of violence and least likley to commit it in TV programs. Heavy viewing of television and its violent programs promotes feelings of "fear and mistrust" about real-life society, according to the survey.

Children, it was found, were "especially vulnerable" to a TV view of the world as a hostile and dangerous environment.