President Barack Obama has warned Uganda's President Yoweri Museveni that enacting an anti-gay law would complicate relations with the US.
Under the proposed legislation, those convicted of homosexual acts could face life imprisonment.
The law would also make it a crime not to report gay people.
President Museveni last month refused to sign the bill but on Friday indicated that he would approve it shortly, after receiving scientific advice.
Ugandan Government spokesman Ofwono Opondo said a team of Ugandan scientists asked by the president for a report on homosexuality had told the president that "there is no definitive gene responsible for homosexuality".
He told the AFP this meant "homosexuality is not a disease but merely an abnormal behaviour which may be learned through experiences in life".
Opondo said the president was under strong domestic pressure to sign the bill.