Americans in the nation's biggest cities killed each other in record numbers this year, a rise in carnage police blame on guns, drugs and a declining reverence for human life.

Not all cities had increased killings, but the number of homicides in the 20 largest cities in 1990 has surpassed the 1989 total by 3 percent, and the year is not yet over. Police in those 20 cities have recorded 7,698 homicides so far this year.New York City recorded its 2,000th violent death of the year last weekend, when seven people were killed in one night. The city had long since surpassed its old record of 1,905 homicides, set just last year.

The Washington, D.C., mark of 434 homicides fell late last month, making it likely that the nation's capital, which has the highest per-capita homicide rate, would remain the murder capital as well.

Homicide records have been set in Dallas, Phoenix, San Antonio, Memphis, Milwaukee, Boston and New Orleans, according to the latest statistics compiled by police in those cities. New marks also were set in Richmond, Va., in Providence, R.I., Bridgeport, Conn., and Oakland and Fresno, Calif.

In most big cities, police say young black men are causing - and bearing the brunt of - the increase in violence.

In 1990, young urbanites killed for drugs, for clothes, for pittances of cash, for love, for hate and just for fun. They killed friends, relatives and innocent bystanders. They turned poor neighborhoods into virtual prisons for law-abiding citizens.

"They just don't care," said Lt. Joe Hladky, acting commander of the Los Angeles County sheriff's department homicide division. "It's that disregard for the value of human life that makes you wonder what direction we're going."

James A. Fox, co-director of the National Crime Analysis Program at Northeastern University in Boston, has been tracking homicide statistics dating back to 1976, and believes the current upsurge in homicide can be traced to a "baby boomerang" - the coming of age of the children of baby boomers.

The last big peak in homicides occurred in the early 1970s, when baby boomers reached prime murder age - late teens and early to mid-20s. Now, Fox said, their children are beginning to reach that age.

These young people, Fox said, "have drugs and weapons and a much more casual attitude about human life than their parents."