NBC has reversed its decision and will carry the first presidential debate live on Sept. 25, interrupting prime-time coverage of the Summer Olympics at a potential loss of $8 million in advertising revenues, NBC executives said Tuesday.

Last week, when the date of the first debate between Vice President George Bush and Massachusetts Gov. Michael Dukakis was announced, NBC News President Michael G. Gartner immediately said NBC would stick to its previously stated policy of carrying the debate on a tape-delayed basis rather than interrupt the Olympics.ABC and CBS said they would carry the debate live.

On Tuesday, NBC President Robert C. Wright issued a statement saying NBC had changed its mind and would interrupt the Olympics for 90 minutes for the debate, then return to Seoul, bring viewers up to date and resume live coverage of the Olympics.

Olympic events that evening will include track and field, cycling, swimming, basketball and boxing.