Opponents of nuclear weapons held memorials Saturday on the 43rd anniversary of the nuclear bombing of Hiroshima, and some people who favor a strong defense and nuclear deterrence staged counter observances.

In Hiroshima itself, 50,000 people attended a ceremony in memory of the 78,000 people killed instantly in the world's first atomic bomb attack.Actor Martin Sheen was among 64 people arrested at the Nevada Test Site in an anti-nuclear protest. He has been arrested on trespass charges several times while participating in anti-nuclear rallies, which have been conducted with growing frequency at the desert site.

Energy Department spokesman Barbara Yoerg said 100 to 125 protesters turned out for the peaceful demonstration at the desert site 65 miles northwest of Las Vegas.

The protest came 11 days before a planned major nuclear weapon test that will judge the ability of the United States and Soviet Union to measure the size of each other's nuclear tests.

Most of those arrested Saturday were cited after they crossed a cattle guard on a road leading to the main gate of the secret site. Some were arrested after they crawled over barbed wire fences near the entrance to the 1,350-square-mile area. All those arrested were cited for misdemeanor trespass and released after booking.

About 60 people demonstrated at a General Electric aerospace plant in Philadelphia in an observance organized by the Brandywine Peace Community, a religious peace group.

At Indianapolis, people who believe the bombing of Hiroshima was necessary to end World War II and save many lives gathered at the Indiana World War Memorial during the morning for prayers and a short ceremony.

Kathy Nikou, Indiana spokeswoman for the Washington, D.C.-based Center for Peace and Freedom, said the bombing saved lives because otherwise it would have been necessary to take over Japan island by island.

A second Indiana group gathered later Saturday to hold a Japanese peace lantern ceremony in protest of the bombing.

Residents of Portland, Ore., awoke Saturday to find the pavement scattered with thousands of pale "shadows" painted by anti-nuclear activists in memory of the bombing of Hiroshima.

About 150 participants in the Shadow Project claimed to have whitewashed 2,700 human and animal silhouettes on streets and sidewalks in the 3 1/2 hours before dawn.