As a header, it needs to be concise and to the point. I don't think that literal rendering will work here. 'Stewardship' has a very specific 'feel' in English. Akiva is technically correct, but it simply doesn't have that feel in Hebrew. 'Stewardship' is very flowery, and there is nothing of the same nature that I can think of in Hebrew, certainly not kabalat akhrayut (which in any case means 'accountability': a very laudable sentiment, but not really what it says).
Daniel's suggestion is too long, and also imprecise. All the original term means in this context, is 'protecting the environment'. Hence hagana svivatit. The other (longer) phrase then serves to explicate it.

או - התוכנית ל(עידוד) אחריות סביבתית

יש להשאיר את המונח כפי שהוא מופיע באנגלית, מאחר שמדובר בתוכנית מיוחדת לעידוד שמירה על איכות הסביבה


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Note added at 3 hrs (2007-01-21 15:10:45 GMT)
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"an agri-environment scheme" is clearly a tokhnit

See:
http://www.environment.gov.il/Enviroment/Static/Binaries/Art...
Page 31.
I hope this helps.

And how about:
בהגנה על איכות הסביבה
נגן על איכות הסביבה
מגינים על איכות הסביבה
etc.

my understanding of the term "stewardship" in this context is - taking charge of, managing.
I suppose one could also consider - assuming a leadership role in..... - but I did not get that impression from the discussion here.