wp auto adds <br > and <p> tags in posts, how to disable?

I use xmlrpc metaweblog api add new post to wp. Inside the post message, it already contains tags such as <BR />. wp adds more when displaying them because of line returns. so instead of one <BR />, it is <BR /><BR /> back to back. It makes the display strange.

Question:
– how to disable wp feature that automatically add a
for each line feed?
– how to disable wp feature that automatically add a for each two line feeds?