One of the lessons to be learned from the Iran-contra affair is the need for a stable and reliable U.S. foreign policy. Yet, only two months after the hearings have ended, Congress is on the verge of making a tragic foreign policy error by rewriting U.S. policy toward Pakistan, one of this nation's strongest allies in South Asia and the principal conduit for aid to the Afghan freedom fighters.

In the next few weeks, both the House and the Senate will begin to deliberate on a new foreign aid package for Pakistan. Hanging in the balance is a $4 billion, six-year authorization request intended in large part to ease the burdens of Pakistani assistance to the Afghan freedom fighters. Recent allegations that Pakistan is developing a nuclear weapons capability have jeopardized approval of the aid package by prompting congressional opposition to a waiver of the Symington Amendment -- legislation intended to prevent nuclear weapons proliferation by withholding foreign assistance. Opponents are preparing to make any assistance conditional upon on-site inspection of Pakistani nuclear facilities, a condition not imposed upon any other recipient of U.S. aid.

The current furor in Congress follows the recent U.S. indictment of a Pakistani-born businessman, Arshad Z. Pervez, for trying to smuggle 25 tons of contraband steel in violation of U.S. nuclear nonproliferation regulations. Pakistani officials have denied government involvement, cooperated with the United States by issuing a warrant for the only known accomplice and have reaffirmed that they have no intentions of building nuclear weapons.

Despite the questions raised by the Pervez arrest, there is little doubt that Congress is employing a double standard where Pakistan is involved. India and Israel, both suspected to have a nuclear weapons capability, have been effectively grandfathered from the provisions of the Symington Amendment. And neither country is under any particular congressional pressure to sign the Nuclear Nonproliferation Treaty, which would mandate inspections of nuclear installations.

While Pakistan has proclaimed its willingness to sign the NPT -- understandably contingent upon India's becoming a signatory -- India thus far has flatly refused to consider the Pakistani offer. (India, which derives substantial military assistance from the Soviet Union, labors under no nonproliferation conditions on its aid.) Under these circumstances, Pakistan's refusal to accede to current administration and congressional demands for inspection of its nuclear facilities in order to assure the United States of its intentions and capabilities is understandable.

Many of those in Congress behind the effort to place conditions on aid to Pakistan have been strong supporters of the Afghan resistance movement. Yet their actions in withholding assistance from Pakistan would sound its death knell. Pakistan is the main channel through which aid to the mujaheddin flows, and its cooperation is essential to the success of that effort. A suspension of military assistance would seriously cripple the resistance and perhaps fatally weaken its ability to counter Soviet aggression.

Further, Pakistani support of the freedom fighters, which has included acceptance of some 3 million Afghan refugees, is exacting a great internal political, economic and social toll. Withdrawal of U.S. support, therefore, would be doubly tragic, threatening a government whose efforts support important U.S. interests in the region, and ending recent progress toward ending the Soviet occupation of Afghanistan.

More generally, abandonment of Pakistan could lead to a major setback to U.S. strategic interests in South Asia. Pakistan has provided a strong buffer to Soviet regional ambitions, primarily by denying them access to a warm water port. The credibility of Pakistan's defenses, given the country's current arsenal of aging weaponry, would be severely diminished in the absence of U.S. support, resulting in a no-cost windfall to the Soviets.

The ultimate irony of the congressional proposals is that they are likely to prove counterproductive. Withdrawal of U.S. assistance would lessen U.S. power to influence the nuclear debate in Pakistan. Forcing Pakistan essentially to go it alone will only serve to strengthen a significant segment of the population that believes nuclear weapons are the only reliable deterrent to a hostile India in the east -- with 2 1/2 times Pakistan's conventional capability -- and an increasing Soviet threat in the west.

My recent meetings with Pakistani officials underscored the government's commitment to satisfying a range of U.S. concerns. Democratization is proceeding in an orderly fashion, with General Zia having devolved much of his authority to an elected prime minister and others. A number of his outspoken opponents expressed to me their satisfaction with the pace of democratization. Pakistani officials, albeit bitter over what they contend were hasty prejudgments made by Congress, are also cooperating fully in the Pervez case.

Over the past decade, Congress has too often acted impulsively and ignored the long-term consequences of its actions, which often offend foreign friends and bring our reliability as an ally into question. If Congress were serious about curbing nuclear proliferation in South Asia, it would not simply single out Pakistan for special treatment, but aggressively work to make both Pakistan and India signatories to the NPT. The Symington Amendment, however loftily motivated, should be waived in this case, and its general efficacy as a tool in our efforts to curb nuclear proliferation reviewed.

In the wake of Iran-contra, Congress has been demanding a larger foreign policy role. The upcoming debate will tell whether Congress will mandate an uneven and discriminatory policy or take the responsibility for promoting a balanced long-term U.S. foreign policy in South Asia.

The writer, a former Republican senator from Texas, was chairman of the Armed Services Committee.