According to the ACLU, you should not open the door unless agents can prove that they are executing a warrant signed by a judge. If the agents can produce a warrant, instruct them to slip it under the door, and verify that it was issued by a court and signed by a judge.
If agents force their way into your home, do not resist. You should say: “I do not consent to your entry or to you search of these premises. I am exercising my right to remain silent. I wish to speak to my lawyer as soon as possible.”
Everybody inside the home at the time can exercise their right to remain silent.
The ALCU strongly advises against lying or producing false documents.
As always, ask to speak with an attorny before signing any documents.