WASHINGTON (AP) _ Crime fell 4.1 percent to 35.5 million incidents in 1984, the lowest level in the 12-year history of the National Crime Survey of randomly selected American households, the government said Sunday.

The number of violent crimes excluding murder, however, rose 0.9 percent from 5,903,000 in 1983 to 5,954,000 in 1984. These incidents include assaults, armed robbery and rape.

The newest read-out on crime in America was in a report entitled ''Criminal Victimization 1984,'' issued by the Bureau of Justice Statistics, an information-gathering arm of the Justice Department.

Preliminary National Crime Survey victimization figures for 1984, released in April, had shown that overall crime incidents totaled 35.3 million compared to 37 million in 1983. The final 1984 statistics released Sunday showed no significant variation from that.

''Criminal victimizations in the United States dropped by 1.5 million to about 35.5 million in 1984 for persons age 12 and older,'' the report said.

''This decline continued a trend that has now reduced criminal victimizations to their lowest level in the 12-year history of the NCS,'' it added.

The total of 35.5 million ''victimizations'' was 14 percent below the 41.5 million figure recorded in the peak crime year of 1981, it said.

The BJS crime survey does not include incidents of murder and manslaughter. Its results are based on interviews at six-month intervals with people living in some 60,000 randomly selected households. Altogether, around 128,000 people 12 years of age and older were asked whether they were victims last year of various categories of crimes.

Although the survey does not include murder, it is widely regarded by criminologists and law enforcement officials as a broader and more reliable gauge of crime than the FBI's Uniform Crime Reports.

This is because the National Crime Survey counts both crimes that are reported and not reported to police. In fact, the latest survey confirmed a trend of recent years in which only about 35 percent of the crimes are reported to police.

The FBI's Uniform Crime Reports for 1984, released in late July, had shown that nationwide, murders fell by 3 percent compared to the year before.

''It is particularly encouraging that the victimization rate for every major crime we measure with the exception of rape has declined significantly during the past three years,'' said bureau director Steven R. Schlesinger.

''Because the aging of the population can account for only a small fraction of the drop,'' he said, ''much of the decline is most likely the result of increased citizen involvement in crime prevention activities as well as the greater success of law enforcement authorities in apprehending, convicting and incarcerating repeat criminal offenders.''

Although there were decreases last year in a wide variety of crime categories, violent crime showed no improvement compared to 1983, although the rate was 12 percent less than the peak rate in 1981.

The rape victimization rate for females, for instance, was 1.6 per 1,000 last year, compared to 1.3 per 1,000 in the preceding year.

Among the other survey findings were these:

-The victimization rate for crimes of personal theft dropped 7 percent in 1984 to a new low, about 26 below the peak for these crimes, which was recorded in 1977.

-Burglary victimization rates were down 8 percent, and have declined by 31 percent from the peak year of 1974.

-Purse-snatchings declined significantly from a rate of 0.9 per 1,000 people in 1983 to 0.7 per 1,000 in 1984.

-Household larceny continued a downward trend begun in 1979, declining by 6 percent to a 12-year low of 99.4 per 1,000 households.

-Robberies in which the victim was injured occurred at a rate of 1.6 per 1,000, up from 1.3 per 1,000 in 1983.