Households in the northeastern United States constituted the least crime-prone region last year, while households in the West were the most likely to be touched by crime, the federal government said yesterday.

Crime affected 19 percent of the households in the Northeast, 25 percent in the Midwest and South and 30 percent of the households in the West, the U.S. Bureau of Justice Statistics reported.

The differences may be due in part to the concentration in the West of migrants as well as younger people in their mid-teens to early 20s, comprising the age group most likely to commit crime, suggested several researchers, including Alfred Blumstein, dean of the school of urban and public affairs at Carnegie-Mellon University in Pittsburgh.

Nationally, one in four American households experienced a rape, robbery, assault, burglary or theft in 1986, down from one in three households in 1975, the Justice Department agency said.

Although the household crime trend has been down for more than a decade, 1986 was the first year since 1981 in which the percentage of households touched by crime did not decline significantly from the previous year. Last year, 24.7 percent of households were touched by crime, compared with 25 percent a year earlier.

Last year, 5 percent of the households had a member who was a victim of violent crime, 5 percent were burglarized at least once and 17 percent were hit by theft or were the target of attempted theft.