PRESIDENT BUSH is getting bad advice from the lawyers who want him to veto the bill on chemical and biological weapons. It's time to tighten the rules against countries that use these foul devices and the manufacturing companies that help them to do it. With very few exceptions -- Iraq is the most notorious -- the world is now moving to rid itself of these weapons. The United States ought to be leading that movement.

Instead, some of the president's advisers are pressing for a veto on grounds that the bill imposes sanctions that would be mandatory. The administration's lawyers argue that the American response to the use of these weapons ought to be left up to presidential discretion. The bill, they claim, is an infringement on the president's constitutional power to conduct foreign policy.

That's a gross exaggeration. The bill says that if a country uses these weapons, the United States will impose on it a range of penalties affecting its economic and political relations with this country. After a year, the president could lift those penalties. Similarly, if a foreign company helps certain countries build these weapons -- countries that have used them recently, or are preparing to use them or are on the list of havens for terrorists -- that company's products will be banned from the American market. Again, after a year, the president could lift the ban. It's absurd to describe that as interference with the president's control of foreign policy.

This legislation is a response not only to Iraq's use of gas but to the revelations that a number of European companies, particularly in Germany, helped Iraq and Libya build factories to produce gas. The German government also has reacted, tightening its restriction of suspect exports and sharply increasing the penalties for violating them. International cooperation to discourage these weapons is improving. A veto of the bill would suggest to all the wrong people that the United States was losing interest in the subject.

The breadth of congressional support for this bill is impressive. It passed the Senate 92 to 0, and 79 senators have now publicly urged him to sign it. But the president's lawyers are telling him that the next time an army uses poison gas, he might find it expedient to overlook the incident -- as President Reagan overlooked the Iraqi use of gas, first on Iranian troops and then on Kurds who were Iraq's own people. In this bill Congress is saying that it doesn't want poison gas or biological warfare overlooked. That's what this quarrel is about, and this time Congress is right.