This is just a very wild guess, but it could be this:
For more information about it, look it up on the IMDB or all-movie guide.
Once again, I do not know if it is what you are looking for, but it easily could be. It does sound a lot like your description. Anyway, I hope this helps, provide more info if you can think of any.
I could not locate a 1970 movie named "Contamination." The one I think you mean is the 1980 film. There is an alien in that with a big eye, but nothing else matches. It does not come through a portal and no tentacle rape happens. What most people remember about "Contamination" (1980) is the alien avocado egg things that make people explode.