President Mohammad Zia ul-Haq and U.S. Ambassador Arnold L. Raphel were killed Wednesday with 37 other people when their military transport plane exploded and crashed in eastern Pakistan, the government radio reported.

Pakistan Radio and U.S. officials said Zia, Raphel and senior Pakistani military officials were aboard the C-130 military transport when it exploded and crashed after takeoff from the city of Bahawalpur, 450 miles south of the capital of Islamabad and 60 miles west of the Indian border. There was no immediate explanation for the explosion.The radio said Zia, 64, and Raphel, 45 - who only last year was named chief envoy to Pakistan, a major U.S. ally in the region - were killed along with everyone else on board.

Vice President George Bush said in New Orleans "a second American, name not confirmed, also was lost" in the crash. He said Pakistan and the United States have "a very special relationship" and said Zia's death was "a great tragedy."

The crash apparently also killed U.S. Brig. Gen. Herbert M. Wassom, Pentagon sources said on condition of anonymity.

The State Department said the senior U.S. military attache to Pakistan, Brig. Gen. Herbert M. Wassom, 49, of Rockwood, Tenn., was among the 39 people killed in the crash and that there were no survivors.

Pakistani military sources said there were border clashes in eastern Pakistan Wednesday between Pakistani and Indian troops but gave no further details. An Indian Defense Ministry spokesman said he had heard no reports of border fighting.

State Deparumint spokeswoman Phyllis Oakley confirmed the deaths of Zia and Raphel but said she had no information on the cause of the crash. She said the plane had taken the president and the ambassdor to the remote site to view a demonstration of a U.S.-built M-1 battle tank.

"The plane took off at 4:30 p.m. local time and crashed about 10 minutes later at a remote site," she said.

Pakistan Radio said Pakistani Senate Chairman Ghulam Is Haq was appointed acting president, and 10 days of mourning were declared.

The Cabinet went into an emergency session after the crash.

The radio reported that the Pakistani army chief of staff, Gen. Akhtar Abdur Rahman, also was among the dead.

U.N. Secretary-General Javier Perez de Cuellar was stunned upon hearing of the accident, his spokesman said.

"The secretary-general received with great shock the appalling news of the death of the president of Pakistan and the American ambassador," spokesman Francois Giuliani said.

Zia seized power in a bloodless coup in 1977 and put the elected prime minister, Zulfikar Ali Bhutto, on trial for murder. Bhutto was hanged April 4, 1979.

After taking power, Zia turned Pakistan away from democracy with a harsh martial law regime. He strengthened his power through support from Washington.

One challenge to Zia's rule came from Benazir Bhutto, daughter of the prime minister he ordered hanged. She returned to Pakistan in April 1986 after two years of self-imposed exile, vowing to oust Zia and restore democracy to Pakistan. Hundreds of thousands of admirers flocked to welcome her and considered her to be her father's political heir.

But Benazir Bhutto never rallied sufficient support to topple Zia.

Zia was born into a middle-class Moslem family in Jullundur, British India, on Aug. 12, 1924. His father, Akbar Ali, was a clerical officer in the British colonial Indian army.

During World War II, Zia was commissioned into the Indian army in 1945 and fought in Burma, Malaya and Java.

When the subcontinent was granted independence from Britain and became partitioned into Pakistan and India, the Zia family trekked 75 miles across Punjab in Pakistan amid a bloodbath of killing by feuding Hindus and Moslems.

In 1955, Zia graduated from the Staff College in Quetta, Pakistan. In 1963 he attended the U.S. Command and General Staff College at Fort Leavenworth, Kan., and quickly moved up the ranks of Pakistan's army.

In 1976, he was appointed army chief of staff by Bhutto, the man he would later overthrow.

"I was shocked," Zia later said of the appointment. "Shocked, not surprised, when I was selected chief of the army by the former prime minister. There were 10 chaps senior to me. I was just one of the army."

After ousting Bhutto, Zia immediately appointed himself president and chief martial law administrator to quell three months of street fighting sparked by anti-Bhutto rioters.

Zia put Bhutto on trial for allegedly murdering a political opponent and hanged him in Rawalpindi central jail, a short walk from Zia's official residence.

In 1979 Zia announced the restructuring of Pakistani society to conform with traditional Islamic law, meaning Islamic punishments were introduced. Theft could result in the amputation of a right hand. A sane adult Moslem who committed adultery or rape could be stoned to death. Those caught drinking alcohol were liable to five years imprisonment and 30 lashes.