elevator pitch + linear exploration

One question about using step() in R:  it kept every single term in a big expression like poly(a,4) * poly(b,4) rather than only picking out the most important terms in there.  Is there a way to have R (or Python) pick the best terms within that big expression?

Also, as a FYI, I deleted all of the tree commands I was using to predict the residuals from my linear models to figure out what variables to add to my (admittedly exceedingly large) linear regression.
No data gathered yet!  I'm planning to start scraping this weekend, but I guess we'll see how long that takes...