Susan Ford, 21, only daughter of former president and Mrs. Gerald R. Ford, will marry Charles Frederick Vance, a divorced Secret Service agent 16 years her senior, her parents announced yesterday.

The Fords issued a brief statement in Rancho Mirage, Calif., where they live, saying the couple plan to be married there next June.

Vance, who was member of the detail guarding the former president when he met Susan in June 1977, is the son of a retired employer of the U.S. Bureau of Mines. Christine Earley of Reno, Nev. She said she and her husband, John, a retired postal worker, learned of the engagement Tuesday when Vance called to announce the news.

"The Fords were the first to know," said Mrs. Earley, who has not yet met her son's future in-laws. She declined to comment on her son's previous marriage other than to say "you will have to ask Charles and Susan about that".

Her husband, however, said in a later telephone interview that Vance and his former wife, whom he had met while on duty in Hawaii, were divorced this spring. Vance adopted his wife's two children by a previous marriage, according to Earley, and still supports them although they live in Mill Valley, Calif., with their mother.

Earley said "Oh, my yes" when asked whether the demands of Vance's work may have played a part in the breakup of his marriage. "He was gone so much and when he was home, ther was no time to relieve himself of his work."

,Mrs. Earley described her son as "extremely dedicated to the Secret Service, a time-consuming job. My son has worked very hard, sometimes months on end without leave. I'm so glad Susan understands - her father's gone so much of the time, you know."

An aide to Mrs. Ford said there are no plans set for the spring wedding.

"President Ford is doing so much traveling that there has been no time to sit down and discuss any," said Gloria Hill in the Rancho Mirage office.

Mrs. Ford, who is also traveling said yesterday that "she's excited and very pleased," according to Hill.

During her father's administration, candid discussion of Susan Ford's love life by her mother probably prompted more speculation than that about any other presidential offspring in modern times. In a 1975 interview with CBS-TV correspondent Morley Saferthen-First Lady Betty Ford said she would not be surprised if Susan, then 18, would tell her if she decided to have an affair.

In a prepublication condensation of her autobiograhy, "The Times of My Life," currently appearing in Ladies' Home Journal, Mrs. Ford recounts that incident and also credits Susan with persuading her to seek medical treatment for her problems with druhs and alcohol.

Like most daughters of presidents, Susan found that her boyfriends were pulled into the new when she was. One of the first was Gardiner Britt, the son of an Alexandria, Va., car dealer, Ted Britt. Another was Brian McCartney, a member of the ski patrol at Vail, Colo., where the Fords frequently vacationed.

Vance joined the Secret Service in 1965. Before being assigned to the unit protecting the Fords in California, he had been stationed in Washington, Honolulu, San Francisco and Los Anglees.

He was among the late Hubert H. Humphrey's agents in the 1968 presidential campaign. humphrey lost, Vance was reassigned to the detail protecting then-Vice President Spiro Agnew.

"He loved both Hubert Humphrey and Spiro Agnew very much, and still sees Mr. Agnew (who lives in Palm Springs) from time to time," Mrs. Earley said.

In 1976, Vance was assigned to Rep. Morris K. Udall's Secret Service detail for the 11 monyhs that the Arizona Democray sought his party's nomination for president.

"he was just a decent, kind human being. "We became very fond of him," Udall said yesterday, reached at his campaign headquarters in Arizona.

Born in Chicago, Vance grew up in Stockton, Calif., where he was an honor student at St. Mary's High School. He won a scholarship to the University of California at Los Angeles and transferred later to the University of California at Berkeley, graduating in 1964 with a degree in criminology. For a year before going into the Secret Service, he worked for the Oakland police department as a patrolman.

Susan, since leaving college before graduating, has worked successfully as a free-lance photographer. Recently she did the still photos for the motion picture "Jaws II." She lives in Palm Desert, a community near Rancho Mirage, where she owns a condominium.