First Lady Nancy Reagan opened a three-day conference on drug abuse yesterday by telling a group of parents that they are making encouraging progress in their grassroots battle against drugs.

Mrs. Reagan was the keynote speaker at a meeting here of the National Federation of Parents for Drug-Free Youth, an organization founded in May 1980 to educate parents about practical solutions to drug problems in the United States.

She told the parents that they "have been effective in closing down paraphernalia shops, changing laws, monitoring what's going on in the schools and what their children are doing, where they are going, and whom they are seeing."

This contrasts, she suggested, with the 1960s when parents were "ill-prepared" to deal with the emerging drug problem. At that time, she said, "We were as much babes in the woods as our children, perhaps in a way more so . . . . Many parents didn't know enough about drugs to recognize the signs."

Mrs. Reagan, who has visited drug treatment centers in an attempt to call attention to the drug problem, said that parents, working through the national federation, "have shown the professionals that something can be done on a scale larger than previously believed."

The theme of parental responsibility was echoed throughout the day in the panels and presentations that were part of this first annual conference held by the federation, which claims 3,000 affiliates.

The conference, which will continue through Wednesday at the Twin Bridges Marriott, involves parents, lawmakers, medical experts, drug abuse specialists and policy-makers from 43 states, Canada, Bermuda and Sweden.

In one of the early sessions, Bob Kramer, coordinator of the Anne Arundel County Drug and Alcohol Program, described the program's evolution and the role of parents in its success. Vonneva Pettigrew of Washington, D.C., told how ethnic groups have participated in antidrug efforts, such as the battle against paraphernalia shops in the District.

"We are involved in the parent movement and we are fighting drug abuse, as well as the problems of inadequate housing, inadequate recreation facilities and others," Pettigrew said, emphasizing that the drive is not limited to the white middle class. "And we are as effective with what we are doing as other groups."

Pettigrew worked with William H. Brown of the D.C. Congress of Parents and Teachers to organize the battle against paraphernalia shops here. She is scheduled to describe that effort in a session this morning.

Retired Brig. Gen. Robinson (Robbie) Risner, who helped form the Texans' War on Drugs, told how that organization of parents worked to strengthen Texas drug laws. As a result of this effort, Risner said, the legislature enacted five laws that, among other things, increased penalties for drug convictions.

In underscoring the seriousness of the antidrug effort, Risner, who was a prisoner of war in Vietnam for more than seven years, said that the "stakes are higher in this war than any other I have participated in."