PAKISTAN, the place where the United States was going to "draw the line" against further Soviet adventures in the Persian Gulf region, is refusing the part. It sniffs that the offered military aid is at once too small and too conspicuous and the offered security commitment too flimsy. As an alternative, President Zia is now exploring a policy of accommodation with the Soviet Union. He seeks to reassure Moscow that he is not harboring Afghan resistance fighters, and he invites the Kremlin to expand -- peacefully -- its regional role.

There is a sense in which the Pakistani decision is a disappointment to the Carter administration. Its officials, all, had made a major project out of leaping to Pakistan's side after the Soviet invasion of Afghanistan on Dec. 27.Did the United States leap without looking? We would say the administration did the right thing by offering Pakistan a choice. The Pakistanis' first concern, one must assume, is to maintain the integrity of their country against both foreign and internal threats. For larger strategic reasons as well as for the sake of its friendship with Pakistan, that is also the prime concern of the United States. If the Pakistanis choose to pursue it by a twisting diplomatic path rather than by an open partnership with Washington, who can complain? In fact, the Pakistani decision has some advantages for the United States. There is all to much reason to fear that the Zia regime would have taken fresh American arms and used them first against the very non-Punjabi minorities that it needs to conciliate in order to strengthen and legitimize its rule. Regardless, becoming the American surrogate in Southwest Asia would likely expose Pakistan to a countering Soviet encouragement of its smoldering separatist movements, especially among the Baluch people who live on the Arabian Sea. Not an invasion but this sort of ethnic meddling is the real threat the Soviet Union poses to Pakistan, and presumably President Zia's opening to Moscow buys some insurance against it. New American arming, moreover, would doubtless lead Indira Gandhi to tighten an Indian-Soviet vise on Pakistan. And the United States would lose its scant remaining leverage on Pakistan's nuclear bomb program.

Southwest Asia is "new" territory for American strategists. It turns out to be a difficult place to "draw a line": there's not much solid ground on which to draw. Fortunately, the discovery is being made relatively early and before any unwise and irreversible policy choices have been made.