There will be no definitive answer to your question.
There are too many hard-to-measure factors that might contribute to competing definitions of “top” or “strongest”.
According to a National Science Foundation survey, the following were the top 25 U.S. baccalaureate-origin LACs of 2002–11 science & engineering doctorate recipients, adjusted for institution size:
Harvey Mudd (24.4 S&E PhDs per 100 alumni)
Reed
Swarthmore
Carleton
Grinnell
Pomona
Haverford
Williams
Bryn Mawr
Macalester
Hillsdale
Oberlin
Amherst
Lawrence U.
Kalamazoo
Wesleyan
Wellesley
Hendrix
Whitman
Allegheny, Vassar, Bowdoin
Earlham
Mt. Holyoke
Occidental (5.7 S&E PhDs per 100 alumni)
Source: http://www.nsf.gov/statistics/infbrief/nsf13323/
Make what you will of this information.
It may be a useful starting point in identifying LACs that are relatively strong in some science fields …
although of course “science” covers a lot of ground.
Lawrence seems to have a relatively strong physics program;
some of the Keck Consortium colleges might be better choices for earth sciences.
(http://www.keckgeology.org/)
Check out course offerings in your area(s) of interest, faculty bios, and facilities
(as well as the overall ambience of the school, financial aid, etc etc).