Elaborate ceremonies marking the fifth anniversary of the 1978 Marxist coup in Afghanistan were conducted in Kabul last week without significant disruption by guerrillas, but resistance intensified in the provinces, according to western diplomatic reports reaching here today.

Combined Soviet and Afghan Army military units paraded through Kabul last Wednesday before high-level delegations from 10 Communist countries, but Afghan rebel forces, which during the past year have stepped up attacks in the capital, maintained a relatively low profile, the diplomatic reports said.

Two bombs exploded outside the Soviet Microrayon housing project in Kabul, killing or injuring at least five persons. Three buses carrying Afghan youths to a government-sponsored rally on the southern edge of the city were blown up by land mines, resulting in an undetermined number of casualties, according to the reports.

Also, assassinations of Soviet and Afghan backers of the government of President Babrak Karmal were reported to have increased, with at least 30 persons reported killed just before and during the celebration of the April 27, 1978, Soviet-supported coup that toppled Mohammed Daoud.

The most spectacular assassination occurred on April 25 on a bridge over the Kabul River near the sprawling Soviet housing complex, where an Afghan Army officer was shot to death in broad daylight in front of startled passers-by, the diplomatic sources said. His assailant escaped.

Previous observances of major anniversaries of the Marxist government have been marred by more widespread resistance in the capital. Taking into account the intensity of guerrilla activity inside Kabul during the winter, western analysts said they were surprised that the ceremonies were conducted without more incidents.

Outside Kabul, guerrillas sabotaged at least six power transmission towers, knocking out electricity in the capital for several days and disrupting broadcasts of the anniversary celebrations, diplomats in Kabul said.

Travelers from Ghazni, 80 miles south of Kabul, and Mazar-e-Sharif, on the border with the Soviet Union, said both towns sustained major attacks by Afghan rebels on the eve of last Wednesday's observances.