In the back rooms of the White House, there has been serious talk of negotiating a new defense treaty with Pakistan, which would build up the dictatorial regime of President Zia ul-Haq. The intent would be to supply Zia with the weaponry to block Soviet expansion and safeguard American interests in the Persian Gulf area.

Before embracing Zia, President Reagan would be well advised to review the file on Pakistan. He will find that Zia sought American aid in 1978 to consolidate his military coup and defend Pakistan's tense border with India.

The documents will show that Pakistani Ambassador Yaqub Khan delivered an incredible ultimatum to State Department officials in Washington: Unless the United States stepped up its military aid to Pakistan, Zia would negotiate a pact with the Russians.

The Kremlin was delighted to play along with Zia and perhaps rock the U.S. diplomatic boat. Soviet Ambassador Anatolly Dobrynin in Washington "approached Khan and suggested the time had come to expand Soviet-Pakistani relations," a secret report states.

As it happened, the United States did not submit to Zia. In fact, direct military aid was cut off in 1979 after U.S. intelligence determined that Zia was preparing to build a nuclear arsenal.

But since the Iranian turmoil and the Soviet invasion of Afghanistan, Zia has invoked the Russian bugbear again in the hope of extracting money and munitions from the United States. My associates Indy Badhwar and Dale Van Atta have learned that Pakistani agents have been lobbying on Capitol Hill and at the State Department for a massive rearming of Pakistan with American weapons.

But Pakistan has been an unreliable ally. Two decades ago, it undermined the Southeast Asia Treaty Orgainization by forging close ties with one of the alliance's supposed antagonists, Red China, and then closing down the American U2 spy plane bases in Pakistan.

Between 1965 and 1969, the Pakistanis made massive arms deals with the Russians. The flow of Soviet tanks and artillery stopped, not by Pakistan's choice but because the Kremlin judged the country to be both unstable and adventuristic.

In 1971, Pakistan helped to open the bamboo curtain for Richard Nixon who thereby reestablished relations with China. As the price for this diplomatic triumph, Nixon supported Pakistan against India in their last military confrontation, thus alienating the world's largest democracy.

Pakistan showed its gratitude by renewing secret negotiations with the Russians, joining other Moslem nations in denouncing the United States and permitting a mob to ransack the U.S. Embassy in Islamabad for several hours in November 1979.

Yet it is this dubious ally that has now adopted a reproachful air of injured innocence as it tries to wring military aid out of Washington. Zia even had the arrogance to dismiss Jimmy Carter's offer of $400 million in arms aid last year as "peanuts."

Now the Reagan administration is pondering an arms package big enough presumably to avoid the recipients' contempt. Coincidentally, a study sympathetic to Pakistan has been widely circulated within the State Department. It makes the fantastic claim that Zia's human rights record is superior to that of his predecessor, Ali Bhutto, whom Zia framed on murder charges, convicted and hanged -- despite a worldwide outcry.

The study, it turns out, was based on a brief visit to Pakistan by its author, Francis Fukuyama, during which he spent most of his time talking with Pakistani military and intelligence officials. What gives the study importance is that Fukuyama will soon be joining the State Department's elite Policy Planning Group.

In past columns, I have cautioned the new administration against rushing blindly into the arms of General Zia. The warning bears repeating.