Your husband should speak with an immigration attorney about his options to get his green card. Does he currently have any status? How did he enter the US? These are questions the attorney will ask.
You husband will need a one or more waivers to be able to obtain his green card. If he is in El Salvador he will have to do consular processing and submit the waivers at the Embassy/Consulate. His prior deportation complicates his process. I would recommend that you consult with an immigration attorney regarding your husband's situation.
If he was arrested and deported he is now most likely inadmissible, which means if he re-enters without a waiver he could face up to 20 years in a federal prison and then be deported again. As the other attorneys have indicated he needs a good immigration lawyer.