* Space station scheduled to end in 2016

* Shuttle Discovery arrives with new lab gear for station

* Obama space review panel due to deliver report

CAPE CANAVERAL, Fla., Aug 31 (Reuters) - Getting humans to Mars will require medical research on the International Space Station through at least 2020, said the program's lead scientist, presenting a time frame five years beyond NASA's current budget forecast.

Extending the life of the station, a $100 billion project of 16 nations that is nearing completion after more than a decade of construction, was a surprise finding of the presidential panel reviewing the U.S. human space program.

The study team's report was to be delivered to the White House this week but was not expected to be publicly disclosed until mid- to late-September.

The panel also said NASA's $18 billion annual budget, about half of which is spent on human space projects, falls about $3 billion a year short for Constellation, the moon-and-beyond exploration initiative NASA plans after it retires the space shuttle and station programs.

"NASA needs the ISS," program scientist Julie Robinson said. "A six-month stay on the space station is going to be the best analog we're ever going to have for a six-month microgravity transit to Mars in the future."

Scientists looking to develop countermeasures for radiation exposure, bone loss and other effects of long-duration stays in space estimate they will need to keep the station operating until at least 2020 to ensure "that next step beyond low-Earth orbit (will be) a safe step for humankind," Robinson said.

NASA plans to spend about $2.5 billion a year for space station operations through 2015.

Ending it just five years after its completion would rankle U.S. partners Russia, Europe, Japan and Canada, which have invested heavily in the program and are looking for payoffs, members of the Human Space Flight Plans Committee said during public hearings.

Subcommittee chair Sally Ride, a former astronaut, said her group found widespread support for continuing, and even enhancing, the station program into 2016 and beyond.

"We didn't start off with that perspective," Ride said. "We don't think that the deorbit of ISS in 2016 makes sense."

While the NASA and the White House begin examining the panel's recommendations, a 13-member joint station-shuttle crew will soon begin unloading more than seven tons of new laboratory equipment, supplies and spare parts.

The shuttle Discovery and seven astronauts arrived at the space station on Sunday for a nine-day stay.

On Monday, the crew planned to attach the shuttle's Italian-built cargo pod onto the station so it can be unpacked. The container is packed with two new research facilities, a freezer, a spare oxygen generator, a second treadmill and a fifth berth for the station's newly expanded six-person crew.

The last bedroom is scheduled to be flown to the outpost next year.

Discovery is due back at the Kennedy Space Center in Florida on Sept. 10. (Editing by Jim Loney and Alan Elsner)