Muddy Waters, who played a key role in the development of electric blues and rock-and- roll and was the greatest contemporary exponent of the influential Mississippi Delta blues style, died in his sleep early yesterday at his home near Chicago. The singer and guitarist was pronounced dead at Chicago's Good Samaritan Hospital, reportedly of a heart attack. He was 68 years old. Beginning in the early 1950's, Mr. Waters made a series of hit records for Chicago's Chess label that made him the undisputed king of Chicago blues singers. He was the first popular bandleader to assemble and lead a truly electric band, a band that used amplification to make the music more ferociously physical instead of simply making it a little louder. In 1958, he became the first artist to play electric blues in England, and while many British folk-blues fans recoiled in horror, his visit inspired young musicians like Mick Jagger, Keith Richards and Brian Jones, who later named their band the Rolling Stones after Mr. Waters's early hit "Rollin' Stone." Bob Dylan's mid-1960's rock hit "Like a Rolling Stone" and the leading rock newspaper Rolling Stone were also named after Mr. Waters's original song. Mr. Waters played his blues at Carnegie Hall in 1959, and in 1960 he made a triumphant appearance at the Newport Jazz Festival, where he introduced his blues hit "Got My Mojo Working" to white music fans. His music was widely imitated by a generation of young white musicians, and virtually all the leading rock guitarists who emerged in the 1960's, including Eric Clapton, Jeff Beck, Jimmy Page and Johnny Winter, named Muddy Waters as one of their earliest and most important influences. Mr. Clapton returned the favor by hiring Mr. Waters to open the concerts on one of his American tours of the 1970's, where hundreds of thousands of rock fans heard Mr. Waters. Mr. Waters made his final concert appearance last June when he performed his early hit "Blow Wind Blow" in an Eric Clapton show in Miami. But Muddy Waters was more than a major influence in the pop music world. He was a great singer of American vernacular music, a vocal artist of astonishing power, range, depth, and subtlety. Among musicians and singers, his remarkable sense of timing, his command of inflection and pitch shading, and his vocabulary of vocal sounds and effects, from the purest falsetto to grainy moaning rasps, were all frequent topics of conversation. And he was able to duplicate many of his singing techniques on electric guitar, using a metal slider to make the instrument "speak" in a quivering, voice-like manner. His blues sounded simple, but it was so deeply rooted in the traditions of the Mississippi Delta that other singers and guitarists found it almost impossible to imitate it convincingly. "My blues looks so simple, so easy to do, but it's not," Mr. Waters said in a 1978 interview. "They say my blues is the hardest blues in the world to play." McKinley (Muddy Waters) Morganfield was born April 4, 1915, in Rolling Fork, in the southern Mississippi Delta near Highway 61. His father, Ollie Morganfield, farmed and played blues guitar, but his parents separated when he was six months old and he went to live with his maternal grandmother on a plantation outside Clarksdale, Miss., a town in the central Delta where John Lee Hooker and other future blues and gospel stars grew up. His grandmother began calling him "Muddy" when he was a baby because he liked playing in the mud, and when he was a child on the plantation playmates added the surname "Waters." Muddy Waters began making music when he was 3 or 4 years old. He began performing on harmonica at country picnics and fish fries when he was 12 or 13, and had plenty of opportunity to watch older blues singers and guitarists. Robert Johnson influenced him, and so did the impassioned singer-guitarist Son House. But he also listened to commercial blues recordings by Memphis Minnie, Lonnie Johnson, Tampa Red, and Blind Lemon Jefferson on a neighbor's phonograph. In 1941 and 1942, Alan Lomax and John Work recorded Mr. Waters in Mississippi for the Library of Congress. Hearing himself on records encouraged Mr. Waters to try to make commercial recordings, and in 1943 he moved to Chicago. The following year he acquired an electric guitar, and by 1948 his band, with Jimmy Rogers on second guitar, Little Walter on harmonica, and Baby Face Leroy on guitar and drums, was the most popular blues combo working on Chicago's black South Side. He recorded for Columbia records and for Aristocrat in 1948, and his recording career took off after Aristocrat, owned by Leonard and Phil Chess, became Chess Records, with Muddy Waters as its leading blues artist. In the early and middle 1950's, Muddy Waters and his band made a number of records popular with black record buyers, especially in the Deep South and in Middle Western cities with large populations of Southerners, like Chicago and Detroit. The songs Mr. Waters recorded and performed in the 1950's included "Hoochie Coochie Man," "Just Make Love To Me," "She Moves Me," "Mannish Boy," and "Louisiana Blues." His songs, some of which were original while others came from the blues tradition or were written for him by Willie Dixon, are still in the repertories of countless blues and rhythm-and-blues bands in the United States and around the world. He received widespread recognition in the 1970's, including six Grammy awards and a dynamic featured performance in Martin Scorcese's 1978 film "The Last Waltz." Mr. Waters never grew rich from his music, but he was able to work virtually as often as he wanted to, and in recent months he had been taking time off, "enjoying the fruits of his labor," according to his manager, Scott Cameron. He lived comfortably in Westmont, Ill., a Chicago suburb. His most recent albums, recorded for the Columbia distributed Blue Sky label and produced by his longtime admirer, the rock guitarist Johnny Winter, sold better than all but a handful of his earlier recordings, and he was proud of them. "This is the best point of my life that I'm living right now," he said in 1978. "I'm glad it came before I died, I can tell you." He is survived by his wife, Marva; three daughters and one son; four grandchildren and several great-grandchildren.