THE IRISH REPUBLICAN ARMY claimed responsibility Friday for planting a bomb at an international conference on terrorism in central London and said its target was a government minister . . . THE LAUNCH, planned for Friday, of a $30 million Delta 2 rocket carrying a $65 million Global Positioning System military navigation satellite was postponed unto Saturday because of rain and heavy clouds over Cape Canaveral, Fla. . . . A SAN DIEGO TUNA BOAT sank in high seas north of Vancouver Island, British Columbia, Canada, on Friday, and the Canadian coast guard said one person was rescued and four crew members were missing.