I have green card through the asylum !!Should I say I was detained in my county in n-400 ?

Not to worry. You will have the opportunity to "amend" your N-400 prior to the beginning of the interview. On the day of the interview, prior to being placed under oath, tell the interviewing officer the following: "Before we begin, I'd like to amend an answer on my N-400 and straighten the record": I'd like to change my answer to Q (number) on Section (number) to reflect the fact that,just as I explained on my asylum application, I was arrested a d placed in detention.for political reasons, due to the fact that I was a known opponent of the regime....... " I did not list that arrest on my N-400 because at first I was under the mistaken belief that I had to list only arrests in the US and not those abroad...." Officers are used to these types of amendments and no one will think any less of you, quite the contrary!

Mr. Behar is correct ... explain it at the interview.

No problem, you may change and explain your answers at the interview. It is always better to be truthful than to try to conceal anything.