Pakistani army mountaineer troops intensified their attack today on armed tribesmen holding several thousand Chinese construction workers hostage along the Karakorum Highway between Pakistan and China, according to a highly authoritative source.

Thirty Kohistani tribesmen and five soldiers had been killed by yesterday, the source said.

The army has moved as many as 12,000 specially trained troops up the highway, also known as the Silk Route which links Pakistan's Northwest Frontier Province with China's Sinkiang Province, paralleling the Indus River.

About 10,000 tribesmen are believed to have surrounded between 3,000 and 7,000 Chinese road builders in 34 camps along the road.

The Kohistanis, whose leaders are allied with the opposition Pakistan National Alliance, want Peking to force Prime Minister Zulfiqar Al Bhutto to resign. The Alliance has been staging protests against Bhutto, saying the March election that returned him to power was rigged.

Pakistani police arrested a number of opposition leaders in Lahore today. Alliance leader the Pir of Pagaro said 300 were detained in the police reaid.

The arrests were apparently an effort to block a planned "Martyr's Day" protest Friday to honor the more than 250 persons killed in the post-election disorders. A curfew was reimposed in the cities Karachi, Hyderabad and Lahore.

The attacks began yesterday and were building in intensity today. Featuring shelling by 105mm howitzers and 120mm mortars, supported by at least two jet fighters, the assault concentrated on a tribal stronghold near Komilla, 190 miles from the ill-defined Chinese frontier.

Several bridges have been destroyed along the 90 mile stretch of road that the tribesmen control.

The 493-mile highway has been under construction with Chinese assistance since 1969. As many as 40,000 Chinese workers, men and women, arc believed to be at work along the road at any time.

According to an opposition source, rations in the 34 camps ran out two days ago. A jailed Kehistani leader said the tribes' ultimatum for Bhutto to resign has also expired and that the tribesmen would begin kiling Chinese until they achieved their goal.

There has been no way so far to ascertain whether any Chinese has been killed or what the conditions are in the camps.