Mel Blanc, the versatile, multi-voiced actor who breathed life into such cartoon characters as Bugs Bunny, Woody Woodpecker, Daffy Duck, Porky Pig, Tweety Pie, Sylvester and the Road Runner, died of heart disease and emphysema yesterday at Cedars-Sinai Medical Center in Los Angeles. He was 81 years old.

He had been admitted to the hospital on May 19.

In a career spanning six decades, Mr. Blanc helped develop nearly 400 characters and provided a rich mix of voices for some 3,000 animated cartoons. In the 1940's and 50's he supplied the voices for 90 percent of the Warner Brothers cartoon menagerie, and in the 60's he was a co-producer of ''The Bugs Bunny Show,'' an ABC-TV Saturday morning series that featured Looney Tunes characters in new adventures written for television.

In the 1960's he also contributed to ''The Flintstones,'' the first animated situation comedy created for television and the first cartoon broadcast in prime time. For that series he supplied the voices for both Barney Rubble, the dull-witted neighbor of Fred and Wilma Flintstone, and Dino, the Flintstones' pet dinosaur.

Mr. Blanc was still active as he approached 80, when he made new recordings of five of his classic characters for the innovative 1988 live-animation film ''Who Framed Roger Rabbit,'' rejuvenating Bugs, Daffy, Porky, Tweety Pie and Sylvester the cat. Played Three Instruments