The Mars 2003 orbiter would be similar to the veteran Mars Global Surveyor launched in 1996, which is seen here. Photo: NASA/JPL

NASA officials in Washington won't announce on Monday as originally planned whether it will be a robotic orbiter or a lander dispatched to Mars in 2003.

The space agency had issued a press advisory Thursday alerting reporters of a scheduled Monday afternoon briefing at NASA Headquarters where the 2003 plans would be announced.

But on Friday things had changed and another advisory was issued saying a decision had not been made as to what NASA would launch to the Red Planet in 2003.

The statement read: "Dr. Edward Weiler, Associate Administrator, Office of Space Science, Washington, DC, said making the decision was much more complex and difficult than anticipated and that it will take perhaps one to two weeks longer than planned to make the final decision."

The two missions under consideration are a Mars scientific orbiter, which will have a camera capable of imaging objects as small as about two feet (60 cm) across, and a large scientific rover which will land using an airbag cocoon like that on the successful 1997 Mars Pathfinder mission.

Two teams, one based at NASA's Jet Propulsion Laboratory in Pasadena and the other at Lockheed Martin in Denver, conducted separate, intensive two-month studies of the missions to define the and evaluate their likelihood for success, cost and readiness for flight.

Artist's concept of Mars 2003 lander. Photo: NASA/JPL

Weiler has said previously the NASA budget would only support either an orbiter or a lander in 2003, not both.

NASA suffered two back-to-back failures last year when both the Mars Climate Orbiter and Mars Polar Lander were lost while reaching the planet. The setbacks forced the space agency to rethink its entire Mars exploration initiative.