THE NEW TRADE ACT is more than a substantial achievement of economic policy that keeps up the non-Communist world's 30-year momentum toward liberalizing international trade, with all that means for the health and welfare of the nations concerned. It also represents a political triumph - not simply for this administration but for bipartisanship, for executive-congressional collaboration and for the idea of planning in public policy. That is what really made possible the happy signing celebration that Jimmy Carter conducted in the White House Rose Garden the other day.

Actually, the first dollop of credit might best go to the 93rd Congress. With an assist from the Nixon administration , it set out to write new trade legislation correcting tht observed defects of past negotiating and legislative practice. Out of that exercise came the 1974 trade act. It created the authority successive presidents used to negotiate tariff cuts and reduction of non-tariff barriers in the "Tokoyo round." Beyond that - and here is the special point - it set up unique procedures for the conduct of the negotiations and for processing their results into American law. The tradition of bipartisanship in trade legislation had been respected at least since the Smoot-Hawley disaster of the 1930s. To deter crippling diversions and amendments, the 1974 act provided for close and continual executive-branch consultation with Congress (and with the private sector) during the negotiation and during the preparation of the implementing legislation, and for fast-track handling of the legislation once it was prepared.

In the words of the president's special trade representative, Robert Strauss, the act that emerged last Thursday was "precooked." What President Carter and the 96th Congress took out of the oven was put in five years ago by President Nixon and th 93rd.

But the advance planning is not the whole story. A role was played, for instance, by the succession of economic summits, begun by Gerald Ford in 1975, that permitted the key industrialized countries their respective domestic exigencies. The Hill leadership of both parties did yeoman service in bringing about the 90-4 vote of approval for the new bill in the Senate and the 395-7 vote in the House. In the executive branch, passage took an intimate attention to economic detail and a lavish attention to congressional sensibilities and for this the redoubtable Mr. Strauss deserves full marks.

In the end, however, the new law is most of all a tribute to the process by which the United States conducted and followed up the trade talks. In a very real sense, congratulations are due all around.