gouri, I think if the content on a page is pretty low...putting 3 adsense ads at the top may penalize the page even more. But putting those adsense ads at the BOTTOM of a low content page may even help seo ranking slightly.
I think by now, we have to try to think like google.
Advertisers love it when we put their ads all the way at the top and in prime position...but Google, not as much...I don't believe. (even when it's their own ads)