Two nuclear weapons were detonated simultaneously beneath the Nevada desert this morning in a rare experiment carried out only a few times in 43 years of nuclear testing.

The test was conducted 40 miles from the town of Mercury, where 33 Soviet nuclear scientists are preparing for a historic series of joint nuclear experiments later this summer.The devices were detonated at 7 a.m. in a 750-foot vertical shaft drilled in Yucca Flat, about 85 miles northwest of Las Vegas.

Energy Department spokesman Jim Boyer said he felt "very, very slight motion" at a control point 17 miles from ground zero.

The devices tested Wednesday, he said, were "very, very small" and little ground motion could be expected away from the site.

In Golden, Colo., the National Earthquake Information Center measured the magnitude of today's explosion at 3.1 on the Richter scale, spokesman Waverly Person said. A quake of magnitude 3.5 can cause slight damage.