He noted that the offer was made when the defense ministry`s secretary general, Vice Marshal Eris Herryanto, visited the United States last week.
"They are positive about providing more (fighters) though a grant," he told newsmen at his office.
The shipment of 24 used F-16 jets planned for Indonesia have not yet been delivered, though.
Purnomo said the US offer would be discussed and, if approved, would improve the strength of the country`s air force as the number of fighter planes would triple.
"The grant will accelerate the achievement of the defense forces` (TNI) minimum essential force program," he said.
Purnomo said he did not worry about the possibility of the grant being hindered in case President Barrack Obama was not reelected because it had been approved by the US Congress.
Further, Vice Marshal Eris Herryanto did not know how many additional aircraft would be given by the US, but said the planes would have the same specifications as those of the 24 F-16s delivered earlier.
He noted that the capability of the planes would be upgraded to equal that of the F-16 Block 52, and with the upgrading the planes would be able to fly for 15 to 20 years.
By 2014 around 45 aircraft, including fighter or transport planes, are expected to arrive in Indonesia.
To operate the increasing number of fighter and transport planes,
the air force chief of staff`s logistics assistant, Rear Marshal JFP Sitompul, said the Air Force has recruited some 30 pilots annually.
"With the ongoing recruitment, it is believed tens of the planes will be manned," he said. (*)