Gov. Hugh L. Carey yesterday signed a law repealing the harshest features of "Rockfeller drug laws," once the toughest anti-drug statutes in the nation.

The new law, which takes effect Sept. 1, reduces penalties for many types of hard-drug sales and sharply cuts the use of life sentences. It also reduces the sentences of hundreds of people in prison under the laws signed in 1973 by Gov. Nelson A. Rockefeller.

Even legislators who supported the 1973 laws now admit they were as ineffective as Rockeffeller's critics said then they would be.

Hard-drug trafficking still flourishes, and police catch few big-time drug pushers. Because of the stiff penalties of the Rockefeller laws, more people have been standing trial rather than working out plea-bargains, adding to court backlogs. And hundreds of people convicted of selling or possessing small amounts of drugs are serving mandatory prison terms that often are longer than those given to rapists and robbers.

The new law repeals the most publicized aspect of the 1973 laws - mandatory life sentences for anyone convicted of selling any amount of heroin, cocaine, morphine or other "hard" drugs. Only the most serious offenders will be subject to life terms.00