Secretary of Health and Human Services Margaret M. Heckler yesterday disputed the idea that President Reagan has a master plan to use the tax code to force women back into their traditional role of staying home with their children instead of holding outside jobs.

"I don't think the president is trying to do that," Heckler told reporters at a breakfast meeting when asked if Reagan's tax-simplification plan is "tilted" toward nonworking wives in order to discourage mothers from taking outside jobs.

Heckler's comment appeared to disagree with the views of White House communications director Patrick J. Buchanan, who, according to press reports, said last Friday that the tax plan deliberately favors "traditional" families.

In 1940, 16.7 percent of the nation's married women were in the labor force. By 1984 the figure was about 53 percent; for married women with children under 6 years old, it was 51.8 percent.

Some observers believe that several tax plan provisions favor families in which the wife stays home: provisions to increase earned-income tax credits for the poor and to raise exemptions to $2,000 a person, so that low-income families would pay no income tax; the provision to end the special deduction for two-earner families, and the proposed increase in the Individual Retirement Account deduction for nonworking spouses from $250 to $2,000 a year.

But Heckler said most of the changes purportedly favoring traditional families are designed to foster "fairness" and "equity" in the tax code, not to "remake" the family structure. She said that, although the tax proposal has a "pro-family focus," Reagan is "enormously realistic" and realizes that families come in "many shapes and sizes."

Heckler also said that "we expect a decrease" in the poverty rate when figures reflecting economic revival and low inflation in 1984 are made public this summer. She said that, although the poverty rate has risen sharply in recent years, the biggest jump occurred in 1979-80, before Reagan took office. The rate is now "leveling," she said.