The Soviet leadership, it now emerges, was not all sweetness, light and reasonableness in dealing with those foreign leaders who went to Moscow the other week for the funeral of President Chernenko. President Zia Ul-Haq of Pakistan, for example, has just confirmed reports that his meeting with Mr. Gorbachev was marked by some tough Soviet talking, even threats. He was told that if Pakistan continued supporting the Afghan resistance, who have been having a hard time of it of late, Soviet-Pakistani relations would be affected in the most negative way. Neither General Zia nor the West can be sure of exactly what Mr. Gorbachev has in mind. . . But what General Zia must now fear is an intensification of Soviet cross-border intrusions, i.e., the hot pursuit of guerrilla forces, and even bombings in and around Pakistani towns. If the Kremlin has decided to give Afghanistan high priority in an attempt to wipe out the resistance, and cut off its arms supplies, then General Zia is a target for Soviet reprisals. There is no question but that Pakistan is the key guerrilla sanctuary. It is no secret that it is the pipeline for arms arriving from Europe, Egypt, the Persian Gulf and South East Asia. Mr. Gorbachev's threats may be a direct result of Washington's recent decisions substantially to increase arms and money to the guerrillas. He is also making it clear for both domestic and foreign consumption that the Russians are in no hurry to leave Afghanistan.