John Denver, the singer and songwriter who was the voice of wholesome sincerity and simple country pleasures in the 1970's, died on Sunday afternoon when a light plane he was piloting crashed into Monterey Bay in California. He was 53.

Mr. Denver, a licensed pilot who flew jets, aerobatics planes and gliders, was aloft alone in a light, single-engine two-seat fiberglass airplane built from a kit.

Norman Hicks, the Sheriff of Monterey County, Calif., said that eyewitnesses saw the plane flying about 100 yards off the coast of Pacific Grove at an altitude of about 500 feet. The engine stopped, and at 5:27 P.M. Pacific Time, the plane ''fell directly straight down into the water,'' he said. Mr. Denver's body was identified from fingerprints.

Mr. Denver had walked away uninjured from an airplane accident in 1989, when the 1931 biplane he was piloting spun around while taxiing at a northern Arizona airport.

In songs like ''Take Me Home, Country Roads,'' ''Sunshine on My Shoulders'' and ''Rocky Mountain High,'' Mr. Denver portrayed a rural American paradise of natural beauty and unfailing true love. With an earnest, quivering tenor voice and an acoustic guitar, he made music that was all reassurance, using folk and country elements to lend sincerity to pop sentiments.

''My music and all my work stem from the conviction that people everywhere are intrinsically the same,'' he once said. ''When I write a song, I want to take the personal experience that inspired it and express it in as universal way as possible. I'm a global citizen.''

President Clinton paid tribute to Mr. Denver yesterday, saying his ''soaring music'' touched millions and advanced understanding around the world. In a statement issued by the White House while Mr. Clinton was on a South American visit, the President said Mr. Denver ''opened many doors to understanding among nations'' and praised his environmental work.

Mr. Denver's first wife, Annie Denver, for whom he wrote his 1974 hit ''Annie's Song,'' said, ''He wrote very simple, beautiful songs, and he was a complex man.''

She said that after the couple had argued and made up, Mr. Denver wrote ''Annie's Song'' during a 10-minute ride up a chairlift in Aspen, Colo.

''The songs would just come from him, as if he was a vehicle from God that the songs flowed through,'' she said. ''It was a part of him that he wasn't very ego-attached to. The man was driven to write songs.

''The music came out of a very deep place. And oftentimes, out of that deepness, John felt very alone. If you listen to his songs, there's a lot of loneliness there. I don't think John ever really got how much people loved him. John was a romantic in the best sense of the word, and the world can be tough on romantics.''

Mr. Denver reached his commercial peak in the mid-1970's. His ''Greatest Hits'' album, released in 1973, stayed in the Top 200 for more than three years and has sold more than 10 million copies. He has 14 gold albums (selling half a million copies each) and 8 platinum albums (for sales of more than a million copies). During the 1980's and 90's, he continued to perform and record while devoting himself to causes like wildlife and land conservation, alleviating hunger, curtailing nuclear power and exploring space.

Mr. Denver was born Henry John Deutschendorf Jr. in Roswell, N.M. His father was an Air Force pilot and later a Lear Jet flying instructor who taught his son to fly. During the late 1940's and 50's, the family moved to Oklahoma, Arizona, Alabama and Texas. After his grandmother gave him a 1910 Gibson guitar and he took some lessons, Mr. Denver began playing folk songs in high school.

He enrolled at Texas Tech in Lubbock in 1961, majoring in architecture and performing at coffeehouses. In 1964, he dropped out and moved to Los Angeles, where he started to use the stage name John Denver and became a member of the Back Porch Majority, a group overseen by Randy Sparks of the New Christy Minstrels. In 1965, he replaced Chad Mitchell in the Chad Mitchell Trio, a pop-folk group that recorded new and traditional songs and toured the college hootenanny circuit of the 1960's.

Mr. Denver's song ''Leaving on a Jet Plane'' was recorded in 1967 by Peter, Paul and Mary, and it became a No. 1 hit for them two years later. Milt Okun, who was the producer for the Chad Mitchell Trio and for Peter, Paul and Mary, produced Mr. Denver's first solo album in 1969 and continued as his producer or executive producer throughout Mr. Denver's career.

''It wasn't the quality of his voice,'' said Mr. Okun, who first heard Mr. Denver during auditions for the Chad Mitchell Trio. ''It was the enthusiasm and the drive and the perfect intonation, his glorious intonation, and his ability to sing with anybody. As he got older, he really began to sing even more beautifully, coloring his notes with the words.''

In 1971, ''Take Me Home, Country Roads,'' written with Bill and Taffy Danoff, became Mr. Denver's first million-selling single, beginning a streak of hits that lasted through the decade, including ''Rocky Mountain High,'' ''Annie's Song,'' ''Thank God I'm a Country Boy,'' ''Back Home Again'' and ''I'm Sorry.''

Mr. Denver's round face, wire-rimmed glasses and upraised voice were ubiquitous in the 70's. He appeared regularly on television, headlining at least one television special a year from 1974 to 1981 (when he made three) and performing with Julie Andrews, Beverly Sills and the Muppets. His songs were fixtures on pop charts and on radio stations, both pop and country.

While critics dismissed his music as saccharine, the public embraced it. His albums ''Back Home Again'' (1974) and ''Windsong'' (1975) reached No. 1; Cashbox magazine named him the No. 1 album seller and artist in 1974, and Record World magazine named him as the top male recording artist in 1974 and 1975. The Country Music Association made him Entertainer of the Year in 1975.

He started his own label, Windsong, in 1975; its roster included the Starland Vocal Band, led by the Danoffs, which had a No. 1 hit with ''Afternoon Delight'' in 1976. His 1976 television special, ''Rocky Mountain Christmas,'' won an Emmy award as best musical variety special.

Mr. Denver also began his environmental work in 1976, when he started the Windstar Foundation, a nonprofit educational and research group that ran symposiums, built a solar-powered house near Aspen and made films about hunger. ''When he was talking about environment, most people couldn't even spell it,'' said Hal Thau, Mr. Denver's partner and business manager since 1975.

In 1977, Mr. Denver became a movie actor, appearing with George Burns in ''Oh, God!'' He was also named the poet laureate of Colorado. He was the host of the Grammy Awards telecast in 1978, 1979 and 1982.

As musical fashion moved away from the folk-pop of the 1970's, Mr. Denver had fewer big hits. His last major pop hit was ''Perhaps Love,'' a 1981 duet with the opera singer Placido Domingo; his 1981 album ''Some Days Are Diamonds'' was his last gold album. But he continued to record and perform, and he appeared almost yearly on television Christmas specials and in celebrity golf tournaments.

In 1984, he toured the Soviet Union, and he returned to Moscow to make a duet single, ''Let Us Begin (What Are We Making Weapons For?)'' with a Russian pop singer, Alexandre Gradsky. He went back to the Soviet Union in 1987 to perform at a benefit concert for victims of the Chernobyl nuclear reactor disaster.

In 1984, he wrote a song for the Winter Olympics, ''The Gold and Beyond,'' and performed it at the games in Sarajevo. He toured four cities in China in 1992, the first Western artist to do so, and he performed in Vietnam in 1994.

Mr. Denver was a founder of the Hunger Project and was a member of a UNICEF fact-finding delegation that toured African countries suffering drought and starvation. His interest in flying extended to space flight; he was a board member of the National Space Institute.

He volunteered to fly on the United States space shuttle but was turned down. He said the Soviet Union offered to let him fly in its space shuttle for $10 million, an chance he considered but turned down.

Although he continued to perform to enthusiastic audiences in the United States, Europe and Asia, his album sales decreased. In 1993, Mr. Denver appeared in the film ''Walking Thunder'' and became the first nonclassical musician to receive the Albert Schweitzer Music Award for humanitarian work. He published an autobiography, ''Take Me Home,'' in 1994.

Mr. Denver was arrested on Aug. 21, 1993, on drunk-driving charges in Aspen; he pleaded guilty and was sentenced to probation and a $372 fine. Exactly a year later, he was arrested again for drunk driving. His first trial ended in a hung jury, with a retrial scheduled for January 1998.

Mr. Denver, who was divorced twice, is survived by three children, Jessie Belle, Anna Kate and Zachery.

Recently, Mr. Denver had been performing concerts with symphony orchestras, and the resurgence of interest in the 1970's had helped his career. Mr. Okun, his producer, said that Mr. Denver had just received an offer from a major record label. ''He seemed to me to be the healthiest influence in American popular music'' in the 70's, Mr. Okun said, ''as he still does today.''