A top Roman Catholic cardinal this week challenged President Reagan's pledge to reduce the nation's deficit by slashing social programs while holding the line on military spending.

"Military spending should not be insulated when plans for reducing the deficit are formulated," Chicago Cardinal Joseph L. Bernardin told an appreciative audience at Catholic University Thursday night.

Government programs for the poor, such as food stamps, health care benefits and assistance to the disabled "have been cut enough," he said. Government spending for the poor "is less than 10 percent of the federal budget," but since 1980 "it has sustained 33 percent of all budget cuts."

Bernardin, who guided the development of the United States bishops' pastoral letter on nuclear warfare, added that "it is the responsibility of the federal government to provide for the common defense and to promote the general welfare."

The focus of Bernardin's address here was the bishops' current efforts to develop a pastoral letter on the economy, focusing attention on the growing numbers of poor in the nation. The initial draft of that document, made public after last November's presidential election in an effort to minimize the church leader's political role, is expected to go through two more revisions before it is presented for approval next November.

Responding to criticisms of the initial effort that the bishops were not qualified to draft economic policy, Bernardin said in his address here, "Our role is not to design or legislate programs but to help shape the questions our society asks and to help set the right terms of debate on public policy."

He spoke at some length on one aspect of the poverty issue that was only touched on in the first draft of the economic pastoral: the "feminization of poverty."

Citing statistics to show that "poverty is growing fastest among women and children," he said, "Reducing the economic price of motherhood should be a priority for our society."

Two out of three poor adults are women, he said. "Almost half of all poor families are headed by women, and half of the women raising children alone are poor. One in four children under six is poor. . . . "

Bernardin linked the high poverty rate among women to "job and wage discrimination" and the fact that "child care and support fall mainly on women." High rates of divorce and births out of wedlock have increased the number of women who are the sole suport of their children, he said.

"A single parent . . . finds it difficult to stay above the poverty line," he said. "When that parent faces additional obstacles, such as the cost of day care, which can easily take more than a fourth of an average woman's salary, and sex discrimination in employment, the cards are overwhelmingly stacked against her."

Following the adoption of the bishops' pastoral opposing virtually every use of nuclear weapons, Bernardin challenged Catholics to be as concerned about nuclear warfare as about abortion when developing a "consistent ethic of life." Such a view calls the church to "stand for the protection and promotion of life from conception to death -- that it stand against the drift toward nuclear war . . . and that it stand against the trend to have the most vulnerable among us carry the costs of our national indebtedness.

"To stand for life is to stand for the needs of women and children who epitomize the sacredness of life," he said.

The cardinal pointed out that the church must not only carry out direct works of mercy for the poor; the church also has a role "as advocate and actor in the public life of society."

In ministering directly to the hungry and homeless and neglected, "the churches alone cannot meet the social needs of this nation, and we should not try to do so."

A significant part of the church's role, he said, "is to enter the public debate and work for a compassionate, just, social policy."

This is the task the bishops are addressing in their pastoral letters on peace and the economy. "We invite debate and discussion" of the conclusions in these documents, he said. "We know they must be tested in the public arena . . . We have been using the process of successive drafts to stimulate this discussion."