The phrase "lit agents" is short for literary agents. These are professionals who help writers get their work published and negotiate deals with publishing companies. Full definition
He always went with material sent from lit agents or Big Name writers. (writerunboxed.com)
According to former lit agent Nathan Bransford, submitting from another country won't hurt your chances of getting the attention of an American agent. (bekindrewrite.com)
, but there are also some brilliant «unpublished» authors who get overlooked by smug lit agents and editors, simply because the story isn't what they're «looking for.» (goodereader.com)