Swiss and French tests for a poison gas on Iraqi missile warheads appear to have reached results contrary to those from American tests that showed the presence of VX, a deadly nerve agent, diplomats said Thursday.

If the preliminary findings are confirmed, perhaps as early as next week, Iraq is expected to argue that the American tests were rigged to obtain damaging evidence. In June, American experts at a military testing center in Aberdeen, Md., said they had found traces of the banned poison gas.Iraqi officials have already told U.N. weapons inspectors that if there was VX on the missile fragments tested in the United States, the Iraqis did not put it there. Iraq has admitted to loading sarin nerve gas on weapons but not VX.

The tests in Switzerland and France were done after the Aberdeen reports were made public and Iraq demanded further analysis outside the United States.

At the U.N. Special Commission, which has been overseeing the disarmament of Iraq, a spokesman has been saying all week that there would be no comment on the new results until a final report was submitted to the inspectors.

"When we get the results in final, formal form, we will be able to discuss them," the spokesman, Ewan Buchanan, said Thursday.

The London-based Arabic newspaper Al-Hayat said that the results were already in the possession of the Iraqis.

The contradictions between the two sets of tests may raise a number of other questions. The Iraqi warheads under study were discovered early this year at a weapons-destruction site north of Baghdad. Commission officials haggled with the Iraqis for weeks before being allowed to send some metal chunks dug up at the site to the United States for testing.

Other warhead fragments were stored in Iraq by the inspectors, and there is a question whether Iraqis might have had access to them before commission officials returned to collect samples for the second round of tests in Europe.