You should have no problem entering Ecuador directly from the USA. Ecuador does not require any visitor (regardless of their nationality or country of origin) to hold a visa when entering the country for a stay of 90 days or less.
You might need a USA C1 transit visa for your return journey but, from the US Embassy website, it appears that you're exempted if you qualify for the Visa Waiver Program. See here:
http://www.usembassy....visa/niv/transit.html
and here:
http://www.usembassy....new/visa/niv/vwp.html
If in doubt, contact the US Embassy:
http://www.usembassy.org.uk/ukaddres.html
Chris