Alfred Deller, 67, world-famous countertenor, died in Bologna, Italy, Monday following a heart attack. The noted singer, a resident of London, had gone to Bologna to serve as a judge in the Second Medieval International Song Contest.

Mr. Deller, an Englishman, began to attract attention immediately after World War II as the first countertenor in generations to sing medieval, Renaissance, and baroque music in a way that satisfactorily combined musicanship and tone quality.

The countertenor is a high male voice, which, usually through the use of falsetto, approximates the a lto range. It was in common use in England, especially in church music in the 16th and 17th centuries.

With an extraordinary combination of voice, style, and knowledge of musical history, Mr. Deller brought the voice out of disuse into considerable popularity. Organizing the Deller Consort, he made numerous recordings of music from the medieval centuries up to the time of Purcell and Handel, with special attention to the great English madrigalists. Over a dozen of his recordings are listed in current catalogs.

While Mr. Deller's principal interest lay in music of the past, the late Benjamin Britten wrote the role of Oberon in his operatic version of "A Midsummer Night's Dream" specifically for Mr. Deller, who sang in the premiere performances in 1960 and in the subsequent recording.

With Mr. Deller when he died were his wife, Kathleen, and his son, Mark, who was a member of the Deller Consort.