The United States expects to conclude an agreement allowing Pakistan to buy sensitive American technology as a cornerstone of the visit of Prime Minister Mohammed Khan Junejo, who arrived here last night, administration sources said yesterday.

The agreement, which parallels one signed last year with India, contains strong bans on the use of any of the U.S. technology in Pakistan's nuclear program, which administration officials believe is involved in intensified efforts to develop atomic weapons.

The nuclear assurances contained in the memorandum of understanding, which involves the sale of such high technology as mainframe computers and advanced telecommunications equipment, are considered among the strongest that U.S. officials have gotten the Pakistan government to sign. Administration officials emphasized that this agreement will not allow Pakistan to circumvent U.S. nuclear proliferation restrictions.

Despite accusations by the Carter and Reagan administrations and information supplied by Western European governments, the Pakistani government of President Mohammad Zia ul-Haq has been steadfast in its denials over the past seven years that its nuclear program aims at developing atomic weapons.

Nonetheless, a senior administration official, speaking at a White House briefing, said yesterday that U.S. officials will raise their concerns about nuclear proliferation and Pakistan's nuclear program with Junejo.

Noting that President Reagan has certified annually to Congress that "Pakistan does not possess a nuclear explosive device," the official said that "we see no reason at this time to change our conclusion." In carefully worded responses to reporters' questions, the official would not forecast whether the same conclusion could be certified to Congress in October, when the next such presidential statement is required as a condition of U.S. aid.

Pakistan is the fourth largest recipient of American aid, and the Reagan administration has asked Congress to approve a new six-year $4.2 billion package to take effect when the current $3.2 billion program ends next year.

The official said Pakistan has been told "with great frankness" that U.S. aid will be stopped "if they have acquired a nuclear weapon."

U.S. spokesmen would not comment directly on reports that the United States and the Soviet Union recently have engaged in tough talk about Pakistan's nuclear program. State Department spokesman Bernard Kalb said, however, that "the United States remains fully commited to Pakistan's security in the face of continuing military threat from the Soviet Union and the Afghan regime."

The new agreement, allowing Pakistan to buy sensitive U.S. technology to improve the performance of its economy, contains controls designed to prevent the products from slipping into Soviet Bloc nations. Most of the technology is considered useful for civilian as well as military and nuclear purposes.

Like the memorandum of understanding on technology between the United States and India, this agreement with Pakistan will remain secret.

The agreement is seen by Pakistan as a way of cementing its relations with the United States, especially since closer ties have developed over the past year between the Reagan administration and India. The two South Asian neighbors have fought three wars since British India was partitioned and they gained independence in 1947.

Washington Post Staff Writer Don Oberdorfer contributed to this story.