WITHIN THE next month the leadership of Congress expects to finish work on the trade bill. But both the House and the Senate versions, as they were passed last year, contain many grossly protectionist provisions -- an abundant growth of poison ivy among the few remaining flowers. Some of them are sufficiently dangerous that, should they survive the conference, would well justify a veto by President Reagan. Now that the conference is getting down to serious work, it's time to start going through the list. Let's start with the House bill.

The most notorious of its protectionist sections, the Gephardt amendment, calls for trade penalties on any country running an "excessive" surplus with this country. Those surpluses are almost entirely the result of the Reagan administration's economic errors, as most Democrats including Mr. Gephardt are happy to acknowledge. But the House voted to try to shift the blame for the American trade deficit to foreign countries and make them take the responsibility to reduce it. The conference is apparently going to drop the Gephardt language in favor of more careful language in the Senate's bill. But even the Senate revision is a prescription for proceeding by threat and retaliation.

The House bill would massively expand the definition of export subsidies to include natural resources available more cheaply abroad. Since Mexico sells its natural gas below the price in this country, anything made with Mexican gas could be hit with a tariff on entering this country. The definition also includes farm subsidies and would be a disaster for American agricultural exports when other countries adopted the same rule.

The bill would encourage private suits against imports and would make those suits much easier to win than under present law. These sections of the bill promise an explosion of legal harassment and costly litigation by companies fighting foreign competition.

Another patch of poison ivy is the requirement for very extensive public disclosure by any foreigners investing here -- disclosure of a kind very helpful to their American competitors. When the Canadians imposed a screening requirement on foreign investment, the United States rightly protested. Now the House wants to impose even more onerous and damaging procedures on investors in this country.

These examples aren't the full list of the troublemakers in the House bill, but they are enough to show that its reputation as protectionist is not fanciful. As for the Senate bill, we'll turn to it shortly. These kinds of provisions speak of a country on the defensive, unwilling to compete in the world. But American exports are now rising fast. It makes no sense to lead the world back toward a spiral of retaliation and higher trade barriers at a time when this country is again becoming the world's biggest exporter.