The number of major crimes rose 6% in California in the first half of this year compared with the same period last year--mainly because of changes in reporting requirements. "This increase is the result of a new law effective last January that requires police agencies to respond to incidents of domestic violence as alleged criminal conduct," Atty. Gen. John Van de Kamp said. He explained that previously police usually did not write reports on domestic violence in non-arrest cases. Had the reporting requirements not changed, he said, the California Crime Index of major crimes would have increased by only 1.9% over the first half of 1985. He said the number of aggravated assaults jumped from 29,707 to 40,316, giving authorities "a much more realistic picture of just how serious a problem domestic violence represents in today's society." Other major crimes included willful homicide, up 11%; forcible rape, down 1.7%; robbery, down 0.1%; burglary, up 0.9% and motor vehicle theft, up 6.3%.