The first two satellites, put into orbit in March, pass over North Korea twice a day, at morning and night. Placing two more satellites in orbit will enable Japan to photograph North Korea in the afternoon as well, Kyodo News agency said, citing government sources.
"The official decision to launch will be made when a cabinet subcommittee meets in mid-July, the sources said," Kyodo reported.
The new satellites, one with optical imaging and one with radar imaging capabilities, are the same as those already in orbit.
The new satellites were transferred last month to the Tanegashima Space Center in southern Japan, Kyodo reported, and are to be fired into orbit by the Japanese-developed H-2A rocket.
The optical imaging satellite launched in March has proved capable of distinguishing objects on the ground just over one meter (yard) long.
The radar imaging satellite can take pictures even at night and in cloudy conditions. Researchers expect it will be able to distinguish camouflaged vehicles and facilities.
Immediately after the satellites were launched March 28, North Korea denounced the move as an "hostile act" that could trigger a renewed arms race.
Japan defended its programme, saying that it needed the satellites to strengthen its information-gathering capability to ensure national security.