Robert R. Dahlgren, 52, the public affairs director of the Interstate Commerce Commission, died Oct. 19 at his home in Washington. A spokesman for the D.C. medical examiner said the cause of death had not been determined pending the completion of an investigation by the medical examiner.

A former advertising and public relations executive, Mr. Dahlgren had been liaison division director in the Office of the Secretary of Housing and Urban Development from 1973 to 1976. During the 1976 presidential campaign, he was director of spokesman activities of the President Ford Committee.

After the 1980 election, he served on Ronald Reagan's presidential transition team as an assistant press secretary under his close friend, Jim Brady. Mr. Dahlgren joined the ICC after that.

Mr. Dahlgren had met Brady when both were members of the "Greener Gang" at HUD under William I. Greener, a retired Air Force colonel who became a noted Republican spokesman during the Ford administration, and supervised what was by reputation an able and boisterous crew. By all accounts, Brady and Mr. Dahlgren became something of a team. If Brady was the rollicking old pro, Mr. Dahlgren was the straight man. A 1982 Los Angeles Times story described him as "so fastidious he would make an English butler appear seedy."

In 1981, Brady was shot in the head during the assassination attempt on Reagan. It was in those troubled days that the spirit of the Brady-Dahlgren friendship became truly evident. Mr. Dahlgren remained at George Washington University Hospital with Brady's wife, Sarah, during the long hours of that first night, fielding questions from the news media and keeping friends informed of the seemingly ever-changing prognosis.

Mr. Dahlgren stood vigil for Brady during three more bouts of surgery. Mr. Dahlgren and his wife cared for the Brady's 2-year-old son, Scott, keeping him at the Dahlgren home. And when Brady began his recovery, it was Mr. Dahlgren who organized "happy hours" at George Washington University Hospital for Brady and his convivial friends. He also helped organize a foundation to provide financial support for the Brady family.

Brady's physician, Dr. Arthur Kobrine, told reporters that Mr. Dahlgren played a significant role in Brady's recovery. Korbrine told the Los Angeles Times that Mr. Dahlgren seemed to know when to sympathize with the patient and when to push him.

Robert Richardson Dahlgren was born Jan. 6, 1933, in Princeton, Ill. He earned a bachelor's degree in English at Mercer University in Georgia. He was an Army airborne officer during the 1950s before becoming an advertising executive in New York City.

He was advertising manager of the NAHB Journal of Homebuilding, a trade publication, from 1960 to 1963. During the next seven years, he was an account executive with the McCann-Erickson, Doyle Dane Bernbach, and Rumrill-Hoyt advertising agencies.

Mr. Dahlgren moved to Washington in 1970. Before joining HUD in 1973, he was marketing director with Fulton Lewis Productions and served as director of industry relations and public service advertising with the National Alliance of Businessmen. During the Carter administration, he was a Washington public relations consultant.

In addition to his wife, Francesca (Suzy) Dahlgren of Washington, his survivors include two daughters, F. Jordan and Sarah Dahlgren, both of Washington, and two sisters, Barbara Redding of Birmingham, Mich., and Theodora Jones of Mill Valley, Calif.