Bob Geldof, the Irish rock singer who organized Band Aid and started the whole rock-against-famine movement, announced in London yesterday that two giant all-day benefit concerts will be held in London and Philadelphia on July 13. Featuring more than 20 superstar acts, the concerts will be beamed live to an audience estimated at more than 1 billion people, and are expected to raise more than $12 million for Ethiopian famine victims.

Calling the "Live Aid" concerts "a global jukebox," Geldof said the shows at London's Wembley Stadium and Philadelphia's JFK Stadium would be beamed by satellite around the world, including to the Soviet Union and China.

"The most important people in the music world of the past 20 years will be taking part in this event and will be giving their services free of charge," Geldof said at a news conference.

David Bowie, Mick Jagger, Paul McCartney, Elton John, Paul Young, Simple Minds, Duran Duran and the reunited Who are among the high-powered acts scheduled to appear in London. More than 72,000 people are expected to pay $32 each to attend the 10-hour concert.

At the same time, Stevie Wonder, the Cars, Paul Simon, Huey Lewis and the News, Judas Priest, Bryan Adams, Hall and Oates with the Temptations, Santana, Eric Clapton, Neil Young and Billy Ocean and others are scheduled to perform in Philadelphia. Stadium capacity there is 90,000, and tickets will be selling for $35.

Each act will be limited to 22 minutes, alternating back and forth between London and Philadelphia to accommodate set changes.

The Band Aid single, "Do They Know It's Christmas," has already raised more than $10 million for Ethiopian relief, and its American counterpart, USA for Africa, has just begun to disperse some of the $45 million it has raised to combat the devastating effects of hunger in Africa.

"Rock music has highlighted this issue in a way no government has been able to do," said Geldof. "As the situation worsens in Africa, Band Aid has kept millions of people alive. It is not enough just to keep them alive. We must give them a life as well."