The insurance industry will challenge in a news conference today a recent study reporting that the "overwhelming" reason that women live longer than men is heavier cigarette smoking by men.

The industry says its actuarial data, which the companies use to charge men and women different rates, show a different pattern. Womens' groups have been fighting the different rates and premiums.

The study that started it all, published in the July-August issue of Public Health Reports, compared life and death statistics of about 8,000 people in Erie County, Pa., and showed statistically that the difference in longevity between the men and women could be attributed to only two facts--that men smoke more and that younger men die more frequently from homicide, suicide and other violent causes.

If these factors were eliminated, men and women would live to the same age, the study said. Dean R. Gerstein, one of its authors, said that if the information is true, insurance companies should base rates and premiums on smoking, not on sex.

Michael J. Cowell, vice president and chief actuary of the State Mutual Life Assurance Company of America, said statistics from his and other insurance companies appear to show that the difference in life expectancy is affected by smoking, by sex and by other factors such as stress. The insurance industry is pooling data to make these effects even clearer, he said.

State Mutual's statistics cover 100,000 policyholders, Cowell said, and show that at age 32, for example, the life expectancy of a nonsmoking woman is 3.7 years longer than a nonsmoking man.

Cowell said the method used in the Public Health Reports study was flawed because it compared two groups of people that were not carefully matched.

Gerstein said he stood by the new paper and hoped other researchers would reexamine their data to see if the longevity difference might be due to something other than sex.