ISLAMABAD, PAKISTAN, AUG. 6 -- President Ghulam Ishaq Khan, apparently backed by the Pakistani military, dismissed Prime Minister Benazir Bhutto from office today, dissolved the National Assembly and declared a state of emergency.

Bhutto called the action "illegal and unconstitutional" and said she doubted her Pakistan People's Party would be allowed to return to power in new elections Khan pledged would be held Oct. 24. She vowed, nevertheless, to mount popular and international pressure to ensure an impartial vote.

Khan, who cited government corruption, nepotism and abuse of power as grounds for his action, swore in an interim government under the leadership of Ghulam Mustafa Jatoi, who had led the combined opposition parties in parliament. Two dissident leaders of Bhutto's party were also sworn in as interim cabinet members, along with two members of a conservative opposition Islamic alliance.

The dismissal followed a period of rising tension between Pakistan's military, which has ruled the country for 24 of its 43 years of independence, and the Western-educated Bhutto, who is the first woman to lead a predominantly Moslem nation. Her government was the first elected democratically in Pakistan since the 1970s, coming to power after the death two years ago of military ruler Gen. Zia ul-Haq in an unexplained plane crash.

The army took control of the national television station and telephone exchanges today, but Gen. Mirza Aslam Beg, the military chief of staff, said the action was taken to ensure an orderly transition of power and not to seize power.

"We have never been involved in politics, and we will not be involved in politics," Beg said of the army in a brief comment to reporters. Bhutto and many others involved in the country's politics expressed skepticism about that claim.

The state of emergency gives Khan and his caretaker government the power to dissolve the nation's four provincial assemblies, suspend civilian courts, issue decrees and suspend individual rights. The provincial governments, two of which were led by Bhutto's party, apparently will be dissolved and interim chief ministers sworn in. The composition of the interim provincial governments, which control Pakistan's vast bureaucratic machinery, will have an important impact on any elections held in the fall.

Khan read the order dissolving Bhutto's government on national television late this afternoon, saying that "corruption and nepotism in the federal government has reached such proportions that the orderly functioning of government . . . no longer carries public faith and credibility." He said also that Bhutto's government had failed to respect the country's parliament and constitution.

In citing the authority for his move against Bhutto's government, Khan used the same article of the country's constitution as Zia had in May 1988 to oust a short-lived civilian administration. Pakistan's Supreme Court later ruled that Zia's move was illegal because he failed to cite reasons for the ouster.

In his official order and television address tonight, Khanlaid out a long list of complaints against the Bhutto government. Following his television appearance, contingents of army troops appeared at Bhutto's Islamabad residence, the prime minister's secretariat and the civilian intelligence bureau, Bhutto told reporters.

"This is very strange, because if this is a civilian process, then surely normal civilian procedures should have been followed," Bhutto said. "I am waiting to hear more."

The dismissed prime minister said she had no notice that the president, whose constitutional powers are disputed within Pakistan, intended to dislodge her government.

The president's action followed months of ethnic violence in southern Sind Province and disaffection with Bhutto throughout the country spurred by charges of widespread corruption within her government.

In reaction to the news, street celebrations erupted tonight in the Sind cities of Karachi and Hyderabad, where residents have been ravaged by ethnic violence between native Sindhis associated with administration of the province by Bhutto's party and ethnic Mohajirs who opposed her government. Rural Sind, Bhutto's political base, was said by residents to be in a state of shock, but there were no immediate reports of widespread violence.

Some of the violence in urban Sind, including a spate of ransom kidnappings, has been linked to leading figures in the local branch of Bhutto's party. In justifying his dismissal of the government, Khan spoke at length about the troubles in Karachi and the corruption issue. "Political stock exchanges were opened, and political horse trading was indulged in unabashedly," Khan said. "Some sold their consciences for ministries, and some for plots of land. Some mortgaged their loyalties in return for loans, and some for promised gains."

Since late last year, allegations of corruption have been leveled against mayors, provincial ministers, national legislators and federal ministers in Bhutto's cabinet, as well as against key members of the opposition.

The charges have focused recently on Bhutto's husband by an arranged marriage, Asif Ali Zardari, and his father, Hakim Ali Zardari, both Karachi businessmen whose friends and relatives have taken up important posts in the country's financial bureaucracy.

Khan referred indirectly to allegations against the Zardaris several times during his televised address tonight. The president said he was "sure that this action will be supported by everyone who puts national integrity above politics . . . who has the good of the country at heart, who wishes to see democracy -- genuine and clean democracy -- flourish."

Speaking to reporters at her official Islamabad residence tonight, Bhutto said the corruption charges were "false and unsubstantiated" and were insufficient grounds to dismiss her elected government. "The government is accountable before the people and before the courts of law, not before the president on this ground. . . . We have a clear conscience," she said.

Bhutto said she did not feel betrayed by the president, a career civil servant appointed to the post after Zia's death, because "I believe there were other elements that wanted me out." Bhutto has clashed this summer with Gen. Beg over military promotions, questions of corruption, the role of the army in civil society and Pakistan's foreign policy, particularly toward India and Afghanistan.

Beg, the effective chief of Pakistan's 450,000-member armed forces, was present this afternoon at Islamabad's Presidency Hall for the president's announcement and the swearing-in of Jatoi, the new interim prime minister.

Bhutto said in an interview that her last conversation with Beg was about two weeks ago. "We discussed many issues," she said. "They have their own perspective . . . but then the question comes as to what has to be done and who has to decide and be answerable to the people of Pakistan."

Pakistani officials and senior diplomats said Bhutto's problems with the army this summer concerned both substance and ego. In areas of foreign policy, these sources said, there were disagreements about Kashmir and Afghanistan, with elements of the military leadership said to be pressing for a harder line against India and the Soviet-backed Kabul government.

Bhutto's government was said to be resentful over the army's perceived unwillingness to accept direction from the elected civilian government, particularly on Afghan policy, where the Pakistani intelligence service has enjoyed free rein for more than a decade.

Less substantive but more emotional, sources said, was a series of squabbles between Bhutto and Beg in July over army promotions. In one case, Bhutto urged that a retiring senior general's tenure be extended over Beg's objections. "That's not something deeply political -- it's ego," said a senior diplomat in Islamabad.

Bhutto, a Harvard University and Oxford University graduate, spent much of the last decade in exile while Pakistan was ruled by Zia. Zia had ordered the hanging of Bhutto's father, former Pakistani prime minister Zulfiqar Ali Bhutto, following a 1976 military takeover. Benazir Bhutto took office following elections in November 1988, pledging to fulfill her father's promises of democracy and poverty abatement.

Bhutto said tonight that she saw the president's call for new elections in October as "a smokescreen for the fake kind of elections that there were in 1985 when the political opponents were taken out of the field. I don't believe that there will be elections in which {her Pakistan People's Party} will be permitted to contest. But I do believe that pressure should be mounted for these elections to be held."

In a brief statement issued tonight, U.S. Ambassador to Pakistan Robert Oakley said: "Obviously, the United States and the entire world attach great importance to the democratic process here and elsewhere and will be following developments with close attention."