Sikh separatist guerrillas tonight escalated a terrorist campaign by triggering a series of explosions in New Delhi and neighboring Haryana state that left at least 35 persons dead and more than 100 injured in bus depots and train stations.

In the embattled state of Punjab, meanwhile, Sikh guerrillas pressed their terrorist drive against political leaders by assassinating the state president of the opposition People's Party. The slaying touched off sectarian violence there.

The precision-timed explosions in New Delhi and Haryana state appeared to set back efforts by the government of Prime Minister Rajiv Gandhi to negotiate a political settlement of Sikh demands for increased autonomy in the Punjab.

Gandhi, who called the assassination in Punjab "a cowardly act," met with security chiefs and other officials to discuss the coordinated series of explosions. Afterward, restrictions were imposed on gatherings in New Delhi.

The explosions, most of which authorities said originated in booby-trapped transistor radios left on the seats of public buses and trains, represented the most serious escalation of Sikh terrorism since before Indian Army troops stormed the Golden Temple complex in Amritsar last June 6, killing nearly 1,000 Sikh guerrillas.

Sikh anger at the storming of the holiest site of their religion is believed to have led to the assassination of Gandhi's mother and predecessor, Indira Gandhi, by two of her Sikh bodyguards last October.

That, in turn, prompted acts of mob violence by Hindus against the Sikhs in which hundreds were killed and thousands displaced.

In tonight's explosions, at least 14 people were killed and more than 60 injured in 11 blasts in various parts of New Delhi, including bus terminals and train stations crowded with weekend travelers.

Police said the first explosion occurred at the main bus terminus in an Uttar Pradesh State Transport Corp. bus at 7:10 p.m., killing two persons and injuring six.

In the next several hours, the police control room in New Delhi was swamped with calls about additional explosions at public transport centers throughout the city and in adjoining Haryana state. Security forces sealed all exit roads from the capital.

According to reports received in Chandigarh, the common capital of Punjab and Haryana state, transistor radio bombs killed public transport passengers in in the towns of Sirsa, Hissar and Ambala.

In Hissar, according to the United News of India, an explosion was followed by mob violence, resulting in serious injuries to Sikh passers-by.

In Punjab, Choudhury Balbir Singh, a prominent Hindu and outspoken advocate of Hindu-Sikh amity, was gunned down on his farm on the outskirts of the northern town of Hoshiarpur, authorities in the state capital of Chandigarh said.

Sectarian violence erupted in the town following the assassination, resulting in at least one death, and a curfew was imposed by police. Official reports reaching Chandigarh said about 20 shops were burned and some public buses destroyed by mobs, according to the United News of India.

Singh's murder, coupled with attacks in recent weeks on three well-known non-Sikh political leaders and a series of clashes between Sikh separatist guerrillas and police, recalled the wave of terrorism that preceded the Army assault last June on the Golden Temple complex and an extensive military operation throughout the state.

The new wave of terrorist attacks was viewed by Indian government officials as an attempt by radical Sikhs to sabotage efforts by the government to draw moderate Sikhs into settlement talks.

Last week, the longstanding rivalry between militants and moderates in the Akali Dal party, the mainstream Sikh political grouping, flared openly, with both sides claiming the leadership after slain guerrilla leader Jarnail Singh Bhindranwale's father, Joginder Singh, made an apparently unilateral announcement that the established Akali party leadership had resigned. Bhindranwale was killed in the Golden Temple assault.

A confusing series of denials followed from Akali Dal President Harchand Singh Longowal, but Longowal and his backers were viewed as having lost face to the militants at a time when Gandhi was offering unconditional talks to end the Punjab crisis.

A meeting of the People's Party here, led by former Indian prime minister Charan Singh, condemned the assassination of Balbir Singh and said the state party leader had been "the embodiment of Hindu-Sikh amity."

A party statement charged that the central government was "incapable of administering the country or carrying out its rudimentary duty of maintaining law and order." The Punjab People's Party called for a statewide strike Saturday to protest the killing, and urged all Punjabis to wear black armbands and raise black flags.