Unlike benefits that create really strange bedfellows (remember Iggy Pop and Willie Nelson at Farm Aid IV?), the bill for the ''Sting and Jobim and '' show on March 10 at New York's Carnegie Hall had a certain logic. To raise money (the concert brought in about $250,000) for the Rainforest Foundation which seeks to save both the Brazilian rain forest and the people who inhabit it Sting asked some of Brazil's brightest music stars to lend their talents, including Antonio Carlos Jobim, whose song ''Girl From Ipanema'' redefined the samba. Also on hand were Brazilian singers Caetano Veloso and Gilberto Gil, whose pop music broke from Brazilian tradition and got them both forced into exile in the late '60s. (They have since returned.) North American celebrity do-gooders have drawn some flack recently, but Elton John was undeterred. ''There's nothing wrong with caring about this world,'' he said, and sang a duet with Sting on ''Come Down in Time.'' While Jobim allowed that such celebrity causes might be ''naïve,'' a few days earlier Veloso had commented, ''Mocking efforts like this is easier and more naïve than really trying.''