Pakistani officials indicated Friday that they strongly believe sabotage caused the midair plane explosion of President Mohammad Zia ul-Haq's plane Wednesday.

In emphasizing the likelihood of foul play, officials have all but shelved the ideas of an accident causing the fatal explosion that killed Zia, U.S. Ambassador Arnold L. Rafel, U.S. Brig. Gen. Michael Wassom and 27 others.A team of American investigators is to join Pakistani authorities probing the crash, which occurred near Bahawalpur, a city about 60 miles from the Indian border.

The newspaper Nation reported Friday that authorities suspected an explosive device may have been concealed in a crate of mangoes loaded on the C-130 transport plane just before it took off from Bahawalpur.

According to the paper, the fruit may have been presented as a farewell gift to Zia's party, which had just witnessed a demonstration of an American-built M-1 tank on a military field near the city.

The report of the mangoes could not be confirmed with Pakistani authorities. Bahawalpur is known as a mango producing area, where the popular fruits are just now reaching the end of the season.

Meanwhile, Secretary of State George P. Shultz arrived here Friday night to attend Saturday's funeral for Zia. He was accompanied by three members of Congress, State Department aides and Robert Oakley, a National Security Council official who has been nominated to succeed Rafel.

In a brief arrival statement, Shultz said he had come on a "journey of sorrow." He added that the American people would remember Zia, leader of Pakistan for 11 years, "for his tireless efforts to build stability in this part of the world."

The secretary also praised Zia as a "steadfast champion of the Afghan crusade." During his rule, the Pakistan president helped channel massive American and other foreign aid to Afghan resistance groups fighting Soviet-backed troops.

Among the rumors being circulated by Pakistanis as to why Zia may have been attacked is one popular theory that Afghan secret police agents sabotaged the plane as an act of revenge for Zia's support of the Afghan rebels.

Shultz described the American relationship with Pakistan as "an enduring one, and it will endure." He said there was "a strong bipartisan commitment to Pakistan's security and independence."