WASHINGTON, Sept 14 (Reuters) - Germany on Thursday became the 29th country to sign the Artemis Accords, a U.S.-led multilateral agreement meant to establish norms of behavior in space and on the lunar surface.

The signing marks a key addition to a growing slate of countries aligning their space policies and standards of cooperation with the United States, as nations including China and India eye the moon as stage for technological advances and national prestige.

India, which last month became the fourth nation to achieve a soft landing on the moon, agreed to join the Artemis Accords in June but China and Russia have not.

Germany became the latest signatory at the German ambassador's residence in Washington during an event attended by NASA Administrator Bill Nelson and Walther Pelzer, head of the German Space Agency.

"It's a big deal, because Germany is the economic powerhouse of Europe and has been a part of the European space program forever," Nelson told Reuters on Thursday before the signing.

The accords aim to clarify and modernize principles of the widely ratified 1967 Outer Space Treaty by urging scientific transparency and establishing rules of coordination to avoid harmful interference in space and on the moon.

The pact is a diplomatic prong of the U.S. Artemis program, which was formed in 2019 with the goal of returning the first crew of astronauts to the lunar surface since 1972. Several short and long-term missions in the program aim to use the moon as a proving ground for spacecraft ahead of more difficult astronaut treks to Mars in the future.

NASA has marshaled global allies and an array of private companies around the Artemis program to put NASA astronauts on the moon by 2027, a target that has been delayed from 2024 and is likely to be pushed back again amid spacecraft development delays.

Russia, an integral partner of NASA's on the International Space Station, had considered participation in the Artemis program before instead agreeing to join China's moon program, which also seeks to put humans on the lunar surface.

Japan, various European countries and other nations with big to small space programs have joined the accords. The European Space Agency (ESA), which represents 22 member states including Germany, is a core NASA partner on Gateway, a planned space station that will orbit the moon as part of the Artemis program.

"It's vital to demonstrate unity and solidarity, and Germany signing signals unification among the pillar nations of ESA," Mike Gold, NASA's former international affairs chief and a key architect of the accords, told Reuters.