ISLAMABAD, Pakistan--Benazir Bhutto '73 became the first woman to lead a Moslem nation when the president chose her yesterday to be prime minister, the post her father held when he was deposed and hanged a decade ago.

President Ghulam Ishaq Khan said in a televised address that Bhutto had "the best qualities of leadership and foresight as a statesman."

Thousands of supporters celebrated in streets of the nation's cities after the long-awaited announcement. They danced, beat drums and chanted "Long live Benazir!"

Bhutto's party gained 12 more seats in the National Assembly when it voted Wednesday on candidates to fill 20 seats reserved for women.

With those her populist Pakistan People's Party won in the Nov. 16 election, it holds 105 of the chamber's 237 seats, and she is said to have enough support among minor parties and independents for a majority coalition.

President Reagan sent a letter of congratulations expressing "his hope that the recently conducted elections will usher in an era of democratic rule in Pakistan," a close ally of the U.S., presidential spokesperson Marlin Fitzwater said in Washington.

Zulfikar Ali Bhutto founded the Pakistan People's Party. In 1977, after a landslide victory in the last previous free election, Gen. Mohammed Zia ul-Haq ousted him in a coup.

Bhutto was convicted of complicity in a political murder conspiracy and hanged in 1979. Zia was killed in plane crash Aug. 17 after the election date had been set.

An eight-party grouping called the Islamic Democratic Alliance, which included Zia loyalists, won only 60 seats in the election and Wednesday's assembly vote.

Ishaq Khan, the 73-year-old Senate chair who replaced Zia as president, said yesterday he was convinced Bhutto could command a majority in the National Assembly.

He also declared the end of a state of emergency imposed after Zia's death "so the new prime minister can take up her responsibility in an environment of complete democracy."

The president said he had received the resignations of the caretaker government effective Friday, when Bhutto, 35, was to take the oath of office.