A coalition of groups representing women, blacks, the elderly and organized labor yesterday urged Congress to pass legislation prohibiting the insurance industry from basing insurance premiums or benefits on an individual's gender, race, religion or national origin.

"For too long we have tolerated the insurance industry's practice of imposing group discrimination upon people because they share a common, immutable characteristic . . . ," said Judy Lichtman of the Leadership Conference on Civil Rights, a group of 175 organizations.

"Congress has failed to extend basic civil rights protections to the area of insurance . . . . It is past time to close this unconscionable gap," said Lichtman, who also heads the Women's Legal Defense Fund.

The hearing was held by Senate Commerce Committee Chairman Bob Packwood (R-Ore.), who has proposed legislation to require all private and public pension plans to equalize insurance premiums and benefits for men and women.

Currently, women pay higher costs or receive smaller benefits in a number of pension and health insurance plans. On the other hand, women under age 25 generally pay lower auto insurance rates than men in their age group.

The insurance industry has opposed the Packwood proposal vigorously, arguing that women live longer on the average than men and that it is fair to charge each sex the rate dictated by actuarial tables.

But Packwood said, "It is no longer a valid policy in this country to lump all women together. The day of judging people in this country as a class, rather than as an individual, is coming to an end. It is no longer decent."

Other advocates of the change in the law argued that smoking and obesity contribute more to an individual's mortality rate than the person's gender, but those factors are not taken into account by insurance companies.

"I have one life expectancy as an American, a longer life expectancy as a woman, a shorter life expectancy as one who works in the District of Columbia, a longer life expectancy as a non-smoker, a shorter life expectancy as one who is overweight and who never stays home to go to the doctor," said Mary Gray, president of the Women's Equity Action League.

New York City Mayor Edward I. Koch testified in support of the concept of Packwood's legislation, but he warned that a provision in the bill requiring a pension program to increase benefits to the level of the now-advantaged sex would create serious economic problems for municipal retirement systems. It would, for example, cost New York nearly $1 billion over the next 16 years, Koch said.

"At a time when Congress is working so hard to preserve the future actuarial and financial soundness of the federal Social Security system, it is inconceivable that it would weaken state and local retirement systems by imposing unnecessarily billions of dollars of new liabilities on them," he said.

Koch suggested that the bill be amended to equalize benefits and contributions at a level between the current rates of men and women.

The Supreme Court is considering a case challenging the constitutionality of Arizona's retirement annuity system. Under the Arizona plan, women and men contribute equal amounts, but women collect smaller payments.

The Reagan administration has not taken a position on the pending legislation, but T. Timothy Ryan, solicitor in the Labor Department, said the administration is "dedicated to ensuring fair and equitable treatment for women."