Smoking lava and poisonous gases from a volcanic eruption in central Java claimed at least 155 lives early today in the Dieng Mountains about 200 miles east of here.

Reporters on the scene said most of the victims appeared to have died after inhaling the gas. The area's hospitals, largely ill-equipped for a distaster of this magnitude, are reportedly filled with hundreds more who were overcome by the fumes.

The volcano, Mount Sinila, is near Mount Batur in the Batur district of Central Java Province. Six villages were affected, with Pucukan being hardest hit.

Among the victims in Pucukan were a number of young children on their way to school and Moslems going to mosques for early morning prayers.The volcano was reported to have erupted about 4:30 a.m., following two massive earth tremors earlier in the morning.

In Jakarta, President Suharto ordered a massive rescue effort expected to involve the evacuation of 17,000 persons living in a two-mile radius around the crater. Suharto said about 6,000 have been moved thus far, but efforts have been hampered by lava as deep as 24 feet that has severed one of the main roads giving access to the stricken area.

Few gas masks were available for rescue workers, and several reportedly were killed by the volcanic fumes.

The Dieng Mountains form a plateau about a mile above sea level. The range is peppered with the peaks of about 26 volcanic craters. Areas around the most active peaks have been closed to potential settlers. In fact, the government has moved entire towns and villages from dangerous areas to other Indonesian islands as part of its transmigration program to relieve overcrowding on Java.

Volcanologists at an institute in Bandung, West Java, said today that the Sinila crater was considered dormant and people were allowed to remain in villages near its slopes.

Because of a lack of good roads and medical facilities near the scene of the eruption, officials here fear the death toll will rise.

With an estimated 140 million people, Indonesia is the world's fifth most populous country.About 80 million of them are crowded onto the island of Java.

The Indonesian archipelago has at least 500 volcanoes, 127 of them active, and averages 10 eruptions a year. The deadliest recorded eruption was that of Mount Tambora, on Sumbawa island east of Bali, in 1815, when 92,000 people were killed.

The most famous was that of Krakatoa, said to be nature's greatest modern explosion, on Aug. 27, 1883. Krakatoa and three smaller islands in the Sunda Strait between Java and Sumatra blew up, killing 36,000 persons.