Obama on Monday issued a strong warning to Assad telling him that using those weapons against rebel forces would be “totally unacceptable,” and bring about a U.S. response.
"If you make the tragic mistake of using these weapons, there will be consequences, and you will be held accountable,” Obama said in a speech at the National Defense University.
Secretary of State Hillary Clinton has also said using chemical weapons would be a clear “red line” inviting U.S. action.
Gates on Wednesday said the administration should be ready to follow through on those warnings.
“When the president of the United States cocks the pistol, he better be ready to fire it,” said Gates.
The conflict in Syria has brought international condemnation against the Assad regime, which has used military force to crack down on the civilian population during the uprising.
Efforts at a diplomatic solution, however, have been blocked by Syria’s allies, Russia and China, in the United Nations.
The Obama administration has faced pressure from GOP lawmakers to do more to aid the opposition forces in their struggle. Obama has directed humanitarian aid but has rejected suggestions that the U.S. intervene militarily.
The administration has not specified how it would react to Assad if he uses his chemical arsenal.
Gates said the violence in Syria was likely to worsen as different ethnic groups in the nation fought for power.
“There is a scorecard that those other groups will want to even of massacres and executions. And I think one of the reasons the Alawites and Assad are fighting so hard is that they have some sense of what's likely to happen to them if the opposition is successful in unseating the government in Syria,” he said.