EXCLUSIVE

The sun was barely rising on Kendall Jenner's 18th birthday ... when the top porn companies started offering her lucrative deals ... including one for over a million bucks!

Kendall has been showing off her body for years ... and big sister Kim Kardashian became a household name after her sex-tape with Ray J was released.

And now that Kendall's legal, at least SIX COMPANIES are hoping they can convince her to get it on in front of the camera.

One of the companies -- Bangyoulater.com -- is saying it wants to pay K.J. and a partner of her choosing $1.8 MILLION to bump uglies.

Other interested parties include Brazzers, Babes and Digital Playground ... the latter offering the option of a girl-girl encounter with porn star Jesse Jane.

No word on whether Kendall plans to take any seriously.