THREE RANKING Republican senators yesterday introduced the Economic Equity Act of 1981, an omnibus bill that could have far reaching impact on the economic well-being of American women. The bill proposes reforms in public and private pension law, in tax policy and in insurance and government regulations that will benefit women. Sen. David Durenberger (R-Minn.) called the act he initiated "the instrument by which we will write the next chapter of equality."

It could be that. It most certainly is an opportunity for the Reagan administration to make good on its claim that it is all for economic equality for women. "I would think the Reagan administration would want to leap on this," said Sen. Mark Hatfield (D-Ore.), smiling pointedly at a crowded press conference, "as an offset to the wrongness of their position of the Equal Rights Amendment."

Some provisions of the bill have been introduced before, but never before has such an enlightened and wide-ranging package of reforms enjoyed the backing it has now. Hatfield, who described the poverty of single mothers and of older women as a "a national crisis of great proportions," is the chairman of the Appropriations Committee.Durenberger is on the Government Affairs Committee and on the Finance Committee. The third Senate sponsor, Robert Packwood (R-Ore.), is chairman of the Commerce Committee and a member of the Finance Committee. A similar package was introduced in the House yesterday by the Congresswomen's Caucus and both legislative efforts have bipartisan support. This is legislation that can help both homemakers and women in the labor force. It is mercifully free of the emotionally divisive aspects that have doomed legislative efforts on behalf of women in the past.

One of the most significant aspects of the legislation would be its treatment of marriage as an economic partnership. Hatfield is sponsoring a section that would allow spouses of those in the military and civil service who had been married at least 10 years to receive a pro-rata portion of the worker's pension in divorce settlements, subject to court review. The Economic Equity Act also would prevent military employes from opting out of survivors benefits programs without informing their spouses.

Pension reforms include changes in the private pension systems so that a woman whose husband dies shortly before his retirement can receive some benefits. A "Breaks-in-service" provision would allow employes to take leave to have children and then return to their job without losing time toward their vesting requirement. It also decreases the age for participating in a pension plan from 25 to 21, a significant item for women since they have their highest participation in the labor force in their early 20s.

The bill would outlaw discrimination based on sex in the insurance industry, while another section of the bill would eliminate inappropriate gender-related language from certain armed forces laws.

Packwood's section of the bill would allow employers to provide child care assistance as a tax-free fringe benefit, the way they are now allowed to do with life and health insurance, legal insurance, and educational expenses. The assistance could be a direct payment by the employer to the employe or could be child care provided by the employer, for which the employer would receive a tax break. Other changes would provide tax credits for employers who hire displaced homemakers and would extend similar tax benefits to single parents and married parents, the thinking being that they have the same costs and responsibilities. Homemakers would be allowed to set up individual retirement accounts. A Durenberger provision would provide relief for the widows of farmers who, if not named on the title of their property, are suddenly faced with enormous estate taxes.

The Economic Equity Act has been in the making for nine months. "It has been very carefully crafted to meet the needs of American women," says Ann Smith, director of the Congresswomen's Caucus.

It has also been carefully crafted to meet the political needs of the times. While the government may lose some tax revenue, nothing in the bill requires government spending or government regulation. Nothing in the bill involves the government in day care. On the contrary, the sponsors have tailored a bill that gives individuals new ways of caring for themselves, and provides private employers with incentives to step into the day care gap.

The Economic Equity Act has the support of major women's organizations which have been focusing on economic problems of women. The umbrella bill is expected to be referred to the Finance Committee where it will be broken down into individual titles and referred to individual subcommittees. "It's at that point we think we could get support from some conservatives," says Jenna Dorn, who worked on the bill as a member of Hatfield's staff. Perhaps the best sign for the bill's chances, though, comes from who its sponsors are and where they serve. All of the tax provisions, for example, will be referred to the taxation subcommittee of the Finance Committee and there they are assured of a very friendly reception.

The subcommittee chairman is Sen. Packwood.