Since California and New York are both within the U.S., you will not go through Customs or Immigration at JFK. When you check in for AA4 at LAX, the agent will probably verify your travel documents to make sure that you are eligible to be admitted to Argentina. You should be able to check your bags all the way through from LAX to EZE, so you will not have to leave the secure area at JFK before boarding your flight to EZE.
Since California and New