Undated (AP) _ ISLAMABAD, Pakistan (AP) - Islamic guerrillas have stepped up their offensive against Kabul, bombarding the Afghan capital almost nightly with rockets and fire bombs, Western sources said Tuesday.

They said hundreds of government and Soviet troops have been deployed around the city to try to stop the attacks.

The diplomatic sources, speaking on condition they not be identified further, said reports from Kabul described guerrilla attacks on government and Soviet military installations in and around the city. Government security forces have conducted house-to-house searches across the city to try to unearth guerrilla hideouts and arms dumps, they said.

Islamic guerrillas fighting the Soviet-backed regime began their offensive against Kabul in late July with a major attack on the Soviet air base at the airport. They have hit military positions in and around the capital since then and have fought running battles with troops in the streets, according to the reports.

The Western diplomatic sources said their information from Kabul indicated President Babrak Karmal's government has sent security forces on extensive sweeps through the city to search from house to house for rebel hideouts and arms caches.

The Soviet Union has an estimated 115,000 soldiers in Afghanistan to help fight the Moslem rebellion. Its forces intervened in December 1979, ousting the previous Kremlin-supported government and installing Karmal.

Reports of the fighting cannot be verified independently because Western reporters are barred from the country, which borders Pakistan and the Soviet Union.

The Western sources, who spoke on condition of anonymity, gave this account:

Guerrillas fired missiles last Wednesday night at the headquarters of the 8th Division of the Afghan army near Kharga Lake and a nearby government artillery position. Fighting raged for more than two hours, with Soviet artillery firing repeatedly at suspected guerrilla positions.

The next night, guerrillas fired at least 15 rockets at military targets in the northern part of Kabul, and reports indicated up to 15 government soldiers were killed or wounded.

Rebels fired at least 10 missiles Friday night into and around the Soviet military complex at the Darulaman Palace. Six Afghan soldiers were killed by a missile that exploded near a guard post.

Guerrillas attacked government outposts on the outskirts of the city and overran at least one.

Government and Soviet military commanders responded by strengthening security in the capital and conducting extensive searches. They found at least one cache of heavy weapons.

Army units regularly move through the city in shows of strength and Soviet tanks take up positions at government buildings and installations each afternoon.

Helicopter-borne Soviet troops, supported by helicopter gunships, have carried out search-and-destroy missions in rural areas near the city and Soviet armored columns move out of the city during the day in support.

Soviet helicopters, apparently equipped with special night vision equipment, fly patrols over Kabul at night to help Soviet artillery locate the positions of guerrilla rocket launchers.

Elsewhere in Afghanistan, fighting has tapered off recently in the Panjsher Valley, which is north of Kabul and intersects with the Pakistan border. Rebel forces appear to have withdrawan from the western city of Herat after weeks of fighting in order to avoid encirclement by Soviet and government forces.