B.F. Skinner, 86, one of the foremost figures in modern psychology, whose efforts at applying scientific rigor to the study of behavior raised the man, his techniques and his theories to the status of cultural legend, died of leukemia Saturday in Cambridge, Mass.

A determined and original scientific investigator and a longtime member of the Harvard University faculty, Dr. Skinner also was a philosopher and social theorist whose work was designed not merely to understand human nature, but to foster improvement and bring about a better society.

Dr. Skinner argued that behavior could be modified according to principles discovered by scientific experiment, to build a world without want, free of war and pollution.

Over the years, he won fame for developing such experimental devices as the so-called Skinner Box, an environment in which he studied animals and demonstrated his theories. He also pioneered teaching machines and the associated concepts of programmed instruction.

Books that expounded his views, including "Walden Two," which described a utopian society governed by his theories on the improvement of behavior, brought him renown and followers far beyond his classroom audiences. They made him a cult figure who was particularly popular in the 1960s.

Another book, "Beyond Freedom and Dignity," was on the best-seller list for weeks in the early 1970s.

Dr. Skinner was an adherent of the school of psychology known as behaviorism, which emphasized objective observation of actual behavior rather than focusing on philosophical abstractions such as mind or soul.

"I was determined to become a scientific psychologist," he once said.

Regarded as extreme among behaviorists, he was a controversial figure in modern psychology, and in the wider intellectual world. While honored and revered as one of the most eminent American psychologists, he also found himself frequently under attack by hostile critics.

Some of them viewed his desire to change society through "behavioral technology," with its system of rewards, or positive reinforcement, and punishments, as coldly mechanistic. They saw it as lacking in freedom and free will.

Dr. Skinner's impact on popular culture was not always closely connected to his most profound work.

During World War II, his studies on behavior modification led him to experiment with pigeons in the belief that they could be trained to guide bombs or torpedoes to destroy enemy targets. Although it attracted considerable attention, Project Pigeon was never adopted.

Later, he also taught pigeons to play table tennis.

Asked toward the end of his long career what he might alter if given an opportunity, he said: "Just one thing . . . . I've been laughed at by enemies and kidded by friends. If I could do it all over again, I'd never teach those pigeons to play Ping-Pong."

Burrhus Frederic Skinner was born in Susquehanna, Pa., on March 20, 1904. To the wider world he became known as B.F., but to friends he was Fred.

After graduating second in a high school class of seven, Dr. Skinner received a bachelor's degree from Hamilton College in Clinton N.Y., where he was elected to Phi Beta Kappa and won an award for classical Greek.

Between his junior and senior years, he attended a summer writing school, where he received encouragement from Robert Frost. This led him to spend the year after college at his parents' home in Scranton, Pa., attempting to write fiction.

"I discovered," he said, "the unhappy fact that I had nothing to say."

Influenced by the theories of Russian scientist Ivan Pavlov on conditioned reflexes and by works on behaviorism by Bertrand Russell and psychologist John B. Watson, he began graduate study in psychology at Harvard, where he received his doctorate in 1931.

Long fascinated by tools and gadgets, he developed at Harvard the famed Skinner Box. In the device, closely monitored lab animals are rewarded with food for carrying out simple tasks such as pushing buttons or levers.

The box, which Dr. Skinner preferred to call an "operant conditioning device," is still widely used in psychology and in drug research, where it allows animal reactions to new medications to be observed.

Dr. Skinner conducted research at Harvard for five years after receiving his doctorate, then taught at the University of Minnesota and at Indiana University, where he was psychology department chairman from 1945 to 1948 before returning to Harvard.

After "Walden Two" appeared in 1948, Dr. Skinner said he was "satisfied that I had solved the major problems inherent in the control of human behavior." The latter part of his career has been viewed as representing his effort to specify the problems and their solutions in detail.

In "Science and Human Behavior," published in 1953, he extended his behaviorist theories from the laboratory animals he had so painstakingly observed to man. Four years later, in "Verbal Behavior," he offered a behaviorist explanation of language.

In the 1960s, such works as "The Analysis of Behavior: A Program for Self-Instruction" and "The Technology of Teaching," of which he was a co-author, extended Dr. Skinner's behaviorist principles to the theory and practice of learning.

Although "Beyond Freedom and Dignity," probably his most controversial work, appeared in 1971, Dr. Skinner had evoked protest at least since 1945. In that year a magazine article told of an "air crib" he built for his second child.

It was designed to provide a healthy, stimulating environment for a baby, but some confused readers feared the child was being raised in a Skinner Box.

Dr. Skinner's ailment was diagnosed last year and he was told he would die in a few months.

"I haven't the slightest bit of worry or anxiety about it," he said earlier this month. "I'm not religious, so I don't have to worry about punishment after death."

He said he would be cremated and would give his brain to research.

Survivors include his wife, Yvonne, and their two daughters, Julie and Deborah.

DENZIL "NICK" NICHOLS

D.C. Mortgage Banker

Denzil Oliver "Nick" Nichols, 73, a retired president and board chairman of Frederick W. Berens Inc., a Washington real estate and mortgage banking concern, died of cardiac arrest Aug. 18 at Fairfax Hospital.

Mr. Nichols, who lived in Falls Church, joined Berens in 1949. He rose through the Berens ranks, serving as senior vice president in charge of loans on single-family residences, vice president and treasurer, and executive vice president before becoming president in 1971. He retired as the company's board chairman in 1974.

He was elected president of the Mortgage Bankers Association of Metropolitan Washington in 1971. He was a member of the Washington Real Estate Board and the Homebuilders Association of Metropolitan Washington, and the Greater Washington Board of Trade.

Mr. Denzil, who moved here in 1948, was a native of West Virginia. He attended the University of Louisville. He served with the 1st Marine Division in the Pacific during World War II.

His hobbies included golf and photography.

Survivors include his wife of 40 years, Phyllis D. of Falls Church; a son, Douglas A., of Arlington; two daughters, Susan D. Kipp of Fairfax Station and Robyn A. Nichols of Washington; and four granddaughters.

HOWARD TIHILA

Science Foundation Official

Howard Tihila, 78, who retired in the mid-1970s as administrative services director of the National Science Foundation, died Aug. 18 at a hospital in Clearwater, Fla. He had cancer.

He began his federal government career in 1938. Before joining the science foundation, he worked for the Reconstruction Finance Corp., the Small Business Administration and the Civil Service Commission.

Mr. Tihila, an Oregon native, lived in the Washington area for 50 years before moving to Florida in 1986. He lived in Palm Harbor, Fla.

He was a graduate of George Washington University, where he played fullback on the 1936 and 1937 varsity football teams. He was a Navy veteran of World War II.

Mr. Tihila was a member of Palisades Community Church in Washington and the Chowder and Marching Society.

His wife, the former Mary Cocker, died in 1982. Survivors include a son, Michael, of Ocean City, Md.; two sisters, Aini Duoos and Jean Brunner, both of Astoria, Ore.; two grandchildren; and a great-grandchild.

MARY W. DeGRANGE

Retired Editor

Mary Whitcomb DeGrange, 90, an area resident since 1985 who was a retired New York City editor, died Aug. 15 at the National Hospital for Orthopaedics and Rehabilitation. She had cancer.

Mrs. DeGrange, who had lived at the Hermitage in Alexandria since 1985, was born in Michigan. She received a music degree from Northwestern University.

She settled in the New York City area, where she was to spend more than 60 years. She directed a Works Progress Administration music project in New York during the Great Depression. She later was a music editor for several New York concerns and a publications editor for Columbia University before retiring in the mid-1960s.

Her first marriage, to Robert A. Whitcomb, ended in divorce. Her second husband, Leonard DeGrange, died about 1962.

Survivors include a son by her first marriage, Robert F. Whitcomb of Potomac; four grandchildren; and three great-grandchildren.

MARGARET JOHNSON

Practical Nurse

Margaret Parker Johnson, 79, who was a dietitian and practical nurse at area military hospitals for 43 years before retiring in the early 1970s, died of pneumonia Aug. 16 at Providence Hospital.

She began her career as a dietitian at Walter Reed Army Medical Center. She transferred to Bethesda Naval Hospital in the 1950s and was a nurse there until retiring.

Mrs. Johnson was a native and resident of Washington. She was a graduate of Dunbar High School and attended Howard University.

She was a member of the Catholic Church of the Nativity in Washington.

Her husband of 61 years, Harry Edward Johnson, died in 1988. Survivors include a daughter, Edith M. Belmear, and a half-brother, Theodore Weston, both of Washington; three grandchildren; three great-grandchildren; and a great-great-grandchild.