The target is expected to be in line with figures contained in legislation before the Senate - a reduction of about 17-20 percent from 2005 levels by 2020.
The absence of a US target has widely been seen as the single biggest obstacle to agreement at the summit. President Barack Obama has not yet decided whether to attend the talks.
At the weekend, the hosts of the Copenhagen conference announced that more than 60 heads of state and government had pledged to take part in the two-week negotiating session.
Mr Obama will join them if it appears that his presence would increase chances of the 192 parties reaching agreement, the official indicated.
Administration officials have indicated that the targets are being discussed with senior senators in an attempt to ensure that the Senate will back whatever target Mr Obama takes to Copenhagen.
There will also be pressure internationally for the US to say how much money it is prepared to transfer to poorer countries to help them fight climate change, as it is bound to do under the UN climate convention.