Congressional leaders decided the other day to take another crack at enacting a new trade law this year - without the controversial plant closings notification requirement that prompted President Reagan to veto it.

The new bill, its trade provisions essentially the same as those in the old measure, is expected to come up in the House of Representatives next week. Though the White House has indicated that a trade bill without the plant closings section would be acceptable, there is room for misgivings on this score.Those misgivings were strengthened a few days ago when new figures indicated that the U.S. is reducing the deficit in its international balances of payments by selling more American products abroad.

The latest figures show the trade deficit has fallen 15.5 percent to $9.9 billion, the first single-digit total in nearly three years. What's more, The Washington Post reports that government figures on the trade deficit are much more accurate than they used to be.

In other words, the declining deficit deprives Congress of its excuse for resorting to the protectionist provisions in the revived trade bill.

Among other such provisions, the bill would create whole new categories of vaguely defined "unfair" trading practices, helping domestic companies boot out foreign competitors merely because the U.S. firms cannot match them in price or quality. In fact, the bill would let U.S. businesses be protected for up to eight years even without formal findings of "unfairness." In certain cases it would make U.S. retaliation mandatory - inviting tit-for-tat responses by foreign governments.

Where did Congress get the idea that the way to make American firms more competitive is to shield them from foreign competition? Such protectionism not only antagonizes trading partners, but also penalizes American consumers.

Likewise, how can Congress justify worrying more about the trade deficit than this nation's lawmakers evidently do about the federal budget deficit? The trade deficit is a by-product of the budget deficit, which forces the U.S. to borrow from abroad. When that happens, America has to import more than it exports so that foreigners can earn the dollars to invest here.

Existing law already gives the President of the United States adequate authority to resist unfair trade practices and fight for freer trade. Let's not muddy the waters with protectionist measures that never were necessary and are becoming even less justifiable.