In a 20-year study of how aggression is learned, researchers reported yesterday that lifetime habits of aggressive behavior are already strongly formed in children by age 8.

The most aggressive children learned their behavior from their parents and also from watching violent TV shows early in life, the researchers added.

The study began in 1960 and involved all 875 third graders in Columbia County, N.Y., near Albany.

The researchers said that those rated as the most aggressive at that time were likely to be rated the same way 10 and 20 years later. They also were three times more likely than their less aggressive classmates to be convicted of serious crimes by age 30.

"The most important finding in this work is that children have already formed habits by age 8 that, if nothing is done to change them, will perpetuate into adulthood," said Rowell Huesmann, a psychologist at the University of Illinois at Chicago.

Huesmann was one of four psychologists who presented their findings here at the 91st annual convention of the American Psychological Association. The others were Leopold Walder of Greenbelt, Md., Monroe Lefkowitz of Long Island University and Leonard Eron of the University of Illinois at Chicago.

The researchers started by interviewing the 875 third graders, their classmates and their parents, and then rating the children from most aggressive to least aggressive.

The researchers also studied the parents' behavior toward their children and the habits of the children in detail, including TV viewing.

Followup studies were conducted 10 and 20 years later.

The psychologists said that 23 percent of the most aggressive third graders had been convicted of crimes other than traffic offenses by age 30. Only 9 percent of those rated least aggressive had convictions recorded by age 30.

Factors found to correlate well with high aggression over a lifetime included:

* Harsh punishment, such as being hitwith a belt. The researchers said that further punishment of a child's aggressive The most aggressive children learned their behavior from their parents and also from watching violent TV shows. behavior tended to increase aggression, not diminish it.

* Violence on television. Children who watched the most TV shows with high violence content when they were 8 tended to be those who displayed more aggression later. What 19-year-olds watched on TV did not seem to matter. What they watched as 8-year-olds correlated far better with their aggressiveness than what they were watching currently.

* Neglect or rejection. "The children who can't do anything right in their parents' eyes," as Huesmann put it, are more likely to be aggressive. Parents who completely ignored their child's aggressive behavior also tended to encourage aggression.

The researchers were not measuring assertiveness or competitiveness but such traits as "beating up on other people, interfering directly with other people, any action which injured others, no matter whether it was physical, verbal or stealing from them," Walder said.

Girls were found far less aggressive than boys, and Eron said "the feminists are all wrong" if they suggest that women should act more like men. He said men should be taught to be more like women in some ways.