With its AWACS success behind it, the Reagan administration is now moving with cautious confidence toward a second airplane sales victory. Congress is expected within the next three weeks to approve part of a $3.2 billion economic and military aid package for Pakistan which is to include the sale of 40 F-16 fighter planes to that South Asian nation.
At the same time, however, the administration appears to be divided over the question of another controversial arms sale decision: whether to sell to Taiwan a fighter plane still in the planning stage known as the FX. The possible Taiwan sale is not an issue on Capitol Hill at the moment, but it could become one if the administration decided to go with the sale and Peking then reacted strongly.
President Reagan's victory with the AWACS has clearly not given him an automatic easy ride with Congress on all future foreign policy issues. Several specialists at the State Department and in the Congress said that the AWACS vote was likely to cut two ways: It would convince some senators and congressmen that it was futile to fight the President on foreign policy. But, they said, other senators and congressmen were likely to be looking for issues where they could more effectively express their opposition to administration policies than they did on the Saudi radar plane vote.
Peking, meanwhile, seems to be making sure that if the Taiwan fighter plane sale ever materializes, it will become a major issue. Uncertainty over a possible administration decision on the FX fighter has already created tensions in the Reagan administration's relationship with China. And the Chinese apparently consider this a main topic of discussion for Huang Hua, China's vice-premier and foreign minister, in his meetings here with top administration officials Oct. 29 and 30.
Officials say that US Secretary of State Alexander M. Haig Jr. opposes the sale of the FX or any other advanced aircraft to Taiwan. But some members of the White House staff are said to want to keep the option open. Peking, meanwhile, hints at serious consequences should the Taiwan sale be approved. Some specialists think that such a sale would set US-China relations back several years. Some say, without knowing for certain, of course, that in the event of such a sale China would downgrade its diplomatic ties with the US.
One source said that, in the end, the administration may go for a compromise on Taiwan, refusing to provide new aircraft but agreeing to ''upgrade'' Taiwan's existing squadrons of F-5E fighters. Even such limited move, however, might anger Peking.
Some congressional liberals say that what bothers them most is that the administration seems to be engaging in arms sales - from the AWACS to the Pakistan F-16s - more for the sake of symbolism than anything else. In the case of Taiwan, they say that studies done by the US Central Intelligence Agency and the Defense Department show that Taiwan has no pressing need for new advanced aircraft. According to A. Doak Barnett, a China specialist at the Brookings Institution, China is incapable of invading Taiwan, and tension in the Taiwan region is the lowest since 1949.
When it comes to the Pakistan F-16 sale, liberals say that the administration is attempting to improve relations with Pakistan by providing that country with airplanes which are more sophisticated than those which the Pakistanis actually need. The Carter administration had rejected Pakistani requests for F-16s.
US Rep. Jonathan Bingham (D) of New York, who is chairman of the House Subcommittee on International Economic Policy and Trade, introduced on Oct. 29 a resolution to disapprove the proposed F-16 sale. Given the changed situation following the Soviet invasion of Afghanistan, Mr. Bingham favors some form of security aid to Pakistan but thinks that the F-16s are a symbol, a prestige item , which could end up helping to ''destabilize'' the region.
He and a number of other congressmen and senators are also concerned about Pakistan's reported increasing capacity to produce nuclear bombs. In the Senate, four resolutions have been adopted which would curb aid to Pakistan and other nations should they explode a nuclear device.
Few seem to think that the Congress can stop Pakistan from continuing with its nuclear program, but, according to some specialists, it might be able to get Pakistan to stop short of actually exploding a bomb.
To stop the F-16 sale, both houses of the Congress would have to disapprove. That appears to be an unlikely outcome. But Bingham and others would like to send Pakistan and the administration a signal that their views must be taken into account.
On the Senate side, another resolution of disapproval for the F-16 similar to Bingham's is expected to be submitted, although it is not yet clear who is to be the author. But here, too, the aim is likely to be ''signaling'' more than anything else.