The official Afghanistan Radio reported yesterday that 140 persons were killed and 30 schools destroyed during demonstrations in the last two months against the Soviet-installed Afghan government.

The broadcast, an official version of student demonstrations that rocked the Afghan capital, Kabul, in April and May, indicated that the protests were much more serious than previously reported by travelers from Afghanistan and diplomatic sources in neighboring countries.

In a separate announcements, the radio said 10 key officials and supporters of slain president Hafizullah Amin and one Afghan guerrilla leader had been executed. The 10 included Amin's brother, Abdullah Amin, who had been a provincial governor, and Assadullah Amin, the president's nephew and head of his secret police.

The radio said the rebel executed was Abdul Majid Kalakhani and identified him as a "bandit" who "terrorized the country for the past 10 years."

The announcement of the executions coincided with unconfirmed reports that Moslem rebels were battling Soviet occupation troops at several points around Kabul. In addition, there have been persistent but uncorroborated reports that Soviet troops are gearing up for a major drive against rebel strongholds elsewhere.

The radio's report of casualties and material damage during demonstrations in April and May contrasted with earlier reports that said about 70 high school and university students, half of them girls, were killed and hundreds of others wounded when security forces fired on crowds protesting the Soviet mlitary occupation of Afghanistan.

The protests reportedly began April 21 when students refused to attend ceremonies to present a new national flag. The antigovernment activity was said to have reached a peak April 29 when as many as 5,000 students marched to the former presidential residence, the People's Palace, and began taunting Soviet soldiers guarding it.

The Soviets opened fire on the unarmed students, killing 16 or 17 of them, Afghan witnesses told Washington Post correspondent Stuart Auerbach in New Delhi in May.

During the wave of protests, which continued last month, angry students were said to have killed at least 17 classmates who supported the Communist Afghan government of President Babrak Karmal, lynched a Marxist principal and injured two Soviet soldiers.

In its broadcast yesterday, Radio Afghanistan said "criminals" led by American and Chinese "chauvinists" had disrupted education in Afghan universities and grade schools and were responsible for the 140 deaths and the reported destruction. In addition to the 30 schools allegedly wrecked, the radio said one hospital was destroyed.

The report said that criminals "also have attacked government transport vehicles carrying consumer goods . . . and have blown up warehouses belonging to the public."

The broadcast did not mention any role by antigovernment students in the protests. Nor did it refer to any student casualties or arrests. Diplomatic sources have estimated that about 400 students were arrested during the recent demonstrations.

In a separate report, the Soviet news agency Tass quoted the offical Afghan Bakhtar news agency as saying that about 60 Afghan school children and teachers were hospitalized yesterday after drinking water poisoned by "bandits and mercenaries of imperialism."

Tass said the alleged poisoning was "an inhuman act . . . to intimidate schoolchildren and interrupt their normal studies." It added, "The bandits are turning to the most odious means in attacking children."