Gerard F. Treanor, a defense lawyer who specialized in handling “white-collar crime,” died Oct. 30 at his home in Arlington. He was 70.

The cause was congestive heart failure, said his son, Chris Treanor.

Mr. Treanor was an assistant attorney for the District of Columbia from 1973 until 1977. He then became a founder and partner of Dolan, Treanor, Murray & Walsh, which in 1985 merged with what is now the Washington-based Venable law firm.

He left Venable in 1993 to form his own small firm, Cacheris & Treanor, but returned in 1997 and retired as a managing partner in 2010. He was the first full-time coordinator of the firm’s pro bono department, which he ran for 12 years.

Gerard Francis Treanor Jr. was born in Medford, Mass., and grew up in Washington, where he was a 1961 graduate of St. Anselm’s Abbey School. He received a bachelor’s degree in 1965 from the College of the Holy Cross in Worcester, Mass., and was a 1968 graduate of Catholic University law school.

Mr. Treanor was a law clerk for former U.S. District Judge Edward M. Curran before serving in the U.S. Navy Judge Advocate General Corps from 1969 until 1973.

Throughout his legal career, he represented high-profile clients, including American University President Richard E. Berendzen, who pleaded guilty to making obscene telephone calls to a woman in Fairfax County. During the Monica Lewinsky sex scandal investigation, Mr. Treanor represented Nancy Hernreich, who was Oval Office operations director under President Bill Clinton.

Mr. Treanor was a member of the American College of Trial Lawyers and the National Association of Assistant United States Attorneys. His other memberships included the Society of the Friendly Sons of St. Patrick and Holy Trinity Catholic Church in Georgetown.

Survivors include his wife of 40 years, Sandra Smith Treanor of Arlington; two children, Clare Treanor of Memphis and Chris Treanor of Arlington; his mother, Jeanne Treanor of Washington; three brothers, David Treanor of Olney, Md., Robert Treanor of Amissvile, Va., and Steven Treanor of Brisbane, Australia.

— Megan McDonough