Dr. John R. Fitzpatrick Sr., 85, a retired lawyer and former law school dean who was credited with solving some of this city's most sensational criminal cases as an assistant U.S. attorney here from 1929 to 1934, died Thursday at his home near Frederick, Md. He had a kidney ailment.

In 1918, after teaching school in Omaha, Dr. Fitzpatrick moved to Washington to work for the Commerce Department. He later worked for the State Department and served diplomatic posts in Norway, Sweden, Denmark, England and Canada.

In 1929, he was named an assistant U.S. attorney. He directed several notable extortion investigations, including cases involving a countess and a fashionable girls school proprietress and two brothers who cheated a church rector. He resigned his post in 1934 because of postponement of a murder case.

From 1932 to 1941, he was dean of the Columbus University School of Law, now part of Catholic University. During that time, the school's enrollment quadrupled.

In the late 1930s, he served as special counsel for a House District Committee investigation of criminal conditions in Washington. This resulted in establishment of the Washington Criminal Justice Commission.

In 1937, Dr. Fitzgerald set up the D.C. police department's criminology school, which he operated until 1940.

During World War II, Dr. Fitzpatrick was a lieutenant commander in Naval Intelligence, assigned to Iceland, Egypt, Africa, Syria, Morrocco, Malta, Gibralter and most U.S. bases in the Pacific. He also was commanding officer of the Naval Intelligence School at Frederick, where he made his permanent home.

In 1945, he established a law practice in Frederick, specializing in labor law. He retired in the mid-1970s. He also taught labor law at Catholic University's postgraduate law school.

Dr. Fitzpatrick was born in Dixon, Ill. He a bachelor's degree from George Washington University and bachelor's, master's and doctor's degrees in law from Columbus University.

His wife, the former Elizabeth Kelley, died in 1978.

Survivors include four sons, John R. Jr., of Fairfax, Kelly, of Thurmont, Md., Edmond F., of Millersville, Md., and Richard C., of Frederick; a daughter, Susan Coleman of King George, Va.; a sister, Sister Mary Emmanuel of Dubuque, Iowa, and 17 grandchildren.