The planned detonation of 700 tons of conventional explosives in the Nevada desert next month was postponed indefinitely Friday because of fears over the possible spread of radiation. The detonation site for the blast, known as Divine Strake," is at the Nevada Test Site, which is 65 miles northwest of Las Vegas. The plan was to detonate 1.4 million pounds of fuel oil and fertilizer -- 280 times the amount used in the 1995 Oklahoma City bombing. The prospect has drawn critics, who say the explosion could kick radiation-laced soil into the air, and conspiracists, who say the blast is a front for testing new nuclear weapons.