Washington — The public embrace and warm talks between President Reagan and Pakistani President Mohammad Zia ul-Haq this week are designed to strengthen Pakistan's position as a leader of the nonaligned movement, as a moderating influence within the Muslim world, and as a strong participant in the effort to get the Soviet Union out of Afghanistan.
But it is an embrace that is not altogether comfortable as both countries adjust to a new relationship necessitated by changing geopolitical circumstances.
The United States has softened its rhetoric about Pakistan being a key part of any ''strategic consensus'' to thwart further Soviet penetration in Southwest Asia and the Middle East, for example, a possible base for rapid deployment forces. Relations between Pakistan and India have softened recently. But President Zia must tred a careful path - and one not altogether to US liking - with its other troubling neighbors, Afghanistan, Iran, and the Soviet Union.
The Pakistani position is that the US - more than ever in the two countries' history of roller-coaster relations - must shore up Pakistan. ''In not weakening Pakistan, you are strengthening the stability of the region,'' said one high Pakistani official.
The Reagan administration agrees with this general position and wants to increase dramatically economic and military aid to Pakistan.
But at lower levels within the administration - and especially in Congress - serious questions are being asked of the visiting Pakistanis about human rights, ending the martial law established by President Zia nearly six years ago, and nuclear proliferation. This has put the administration's aid package for Pakistan in jeopardy, and it remains to be seen whether critics in the US will be placated by the Pakistani general's visit.
The Senate Appropriations Committee recently cut requested economic aid to Pakistan for 1983 from $175 million to $120 million, although it approved the administration request for $275 million in military aid. These were to be the first installments in a $3.2 billion, six-year aid program for Pakistan.
There is more opposition to such aid in the House, however, especially to what critics see as the administration's general overemphasis on military assistance. If there is not a change of heart in Congress, administration and Pakistani officials fear, Pakistan may be held under a continuing resolution to 1982 levels of $100 million in economic support and no military sales credits.
This could hinge on the message President Zia is bringing to lawmakers this week.
US intelligence officials estimate that Pakistan could develop a nuclear weapon within four years, given its expanding nuclear energy program, its uranium enrichment efforts, and its refusal to abide by international safeguards against nuclear proliferation. To those raising these points, President Zia insists that ''Pakistan is not interested in manufacturing or acquiring a nuclear weapon.''
The large US military aid package is seen here by administration officials as both stick and carrot to forestall if not prevent Pakistan's developing a nuclear weapons capability. By beefing up that country's conventional military force, it is felt, Pakistan will not feel as great a need to go nuclear. At the same time, it is noted that under US law, aid would be summarily cut off if Pakistan were to explode a nuclear device.
President Zia continues to insist that elections will be held in Pakistan ''when conditions are conducive.'' The people of Pakistan, he told reporters Dec. 8, ''have given very tacit if not direct approval'' of the military regime. Amnesty International and other organizations, meanwhile, continue to highlight human rights violations there.