H. Dale Grubb, 55, a former Secret Service agent, White House special assistant under President Richard M. Nixon, chief congressional liaison officer for the National Aeronautics and Space Administration, died Monday at George Washington University Hospital. He had a heart ailment and diabetes.

Mr. Grubb joined the Secret Service in 1951 and remained in it until 1959. He spent more than two years on the detail assigned to Nixon, who was then vice president. He accompanied Nixon on a trip to Caracas, Venzuela, where the vice president's car was stoned by an unruly mob.

In 1959, he joined the AVCO Corp., an aerospace manufacturer, and became its Washington-area general manager. But he remained in touch with Nixon, traveling with him on campaign trips in 1964, 1966 and 1968. In 1969, when Nixon became president, he appointed Mr. Grubb a special assistant to work on congressional relations.

In 1970, Mr. Grubb was named assistant administrator for legislative affairs at NASA, a position in which he was the agency's top contact with Congress. In 1974, he was appointed assistant deputy administrator of the Veterans Administration, a post he held until 1977.

Mr. Grubb,, who was born in Henryetta, Okla. was a pilot instructor in the Army Air Corps during World War II. After the war, he graduated from the University of Oklahoma, earning a degree in journalism in 1951.

Last year, Mr. Grubb, who lived in Arlington, started a business called the Cherokee Corporation.

He was a past president of the Washington Chapter of the University of Oklahoma Alumni Association, a past president of the Washington branch of the National Space Club and a member of the National Aviation Club, the Federal City Club, the Capitol Hill Club, the Burning Tree Club and the Association of Former Agents of the U.S. Secret Service.

Survivors include his wife, Martha Ann, of Arlington, and three sisters, Cupie Rikard and Juanita Lawler, both of Okmulgee, Okla., and Lola Neel of Santa Rosa, Calif.

The family suggests that expressions of sympathy be in the form of contributions to the George Washington University Hospital Heart Fund.