Judge Gladys Kessler was described by friends and associates yesterday as a cautious, deliberate jurist with a particular concern for the problems of families and children.

Kessler, who yesterday ordered city public school teachers to end their strike or pay stiff fines, "tackles every case with thoroughness and diligence," one courthouse source said.

"Judge Kessler is not a tough judge," another observer said, "but she doesn't let people walk all over her either, especially when it comes to the welfare of children."

Last August, Kessler, who has been assigned to the family division of the court, suprised city officials when she ordered sweeping reforms at Oak Hill and Cedar Knoll, the city's troubled detention facilities for juvenile offenders.

Kessler's wide-ranging order, which has been appealed, outlined job training programs for counselors and other staff members and gave the city 90 days to develop plans to improve the facilities.

Kessler, 40, a graduate of Cornell University and Harvard Law School, was appointed to the D.C. Superior Court bench in June 1977 by President Carter.

From 1969 until her appointment to the Superior Court, Kessler was a partner in the law firm of Roisman, Kessler & Cashdan, where she specialized in public interest law cases. They ranged from consumer lawsuits to women's right advocacy to landlord-tenant suits.

She was the founding president of the Women's Legal Defense Fund in 1971 and was a member of the ethics committee of the D.C. Bar Association from 1974 until her appointment to the bench.

Kessler also has served on the litigation committee of the American Civil Liberties Union, where she earned a reputation for being "cautious, deliberate and wise," according to one attorney.

"In the ACLU we usually win between 80 and 90 percent of our cases," said Ralph Temple, executive director of the Washington chapter of the ACLU."In order to do that, we must be cautious in selecting the cases we take. Judge Kessler was on the committee which determined which cases we would take to court."

Kessler, who has been an appellate attorney for the National Labor Relations Board, also has servtd as a legislative assistant to Rep. Jonathan B. Bingham (D-N.Y.) and executive assistant to Sen. Harrison A. Williams Jr. (D-N.J.).