President Reagan signed an executive order yesterday requiring that federal policies be judged in terms of their potential impact on families, providing a new basis for evaluating welfare, housing and education programs.

"If we would have had this in place a number of years ago, we could have stopped the unintended consequences of some of these well-meaning efforts to help poor families," Gary Bauer, the president's assistant for policy development, said in an interview.

The order, signed by Reagan in California, was the latest of several steps intended to help promote the agenda of conservatives.

Before leaving Washington for his summer vacation, the president announced plans to ban the use of federal funds for abortion counseling and referral. He also announced formation of an interagency task force to encourage adoption as "an alternative for pregnant women" who may be considering abortion. The new executive order empowers Bauer's office to assess how proposed policies would "strengthen or erode the stability of the family and, particularly, the marital commitment."

It also said policies should be judged on whether they "strengthen or erode the authority and rights of parents in the education, nurture and supervision of their children." The order applies to existing and proposed regulations and policies.