BEIJING (Reuters) - China's military said on Sunday it must be governed by the ruling Communist Party and not succumb to "liberal" voices who wish to challenge the party's control.

President Xi Jinping has repeatedly reminded the military to be loyal to the party, as he also steps up efforts to modernize forces that are projecting power across the disputed waters of the East and South China Seas, though it has not fought a war in decades.

In a front-page editorial, the official People's Liberation Army Daily said that "enemy forces" were trying to infiltrate the ranks to push for the "de-politicisation" of the military and remove the party's leadership role.

With a changing society, younger officers are now entering the forces who lack a proper understanding of the party's role and its discipline requirements, the newspaper added.

"When political discipline is firm, then the ruling Party prospers; when political discipline is weak, the ruling Party falls... Liberalism has always been the great enemy of strictly maintaining political discipline," said the paper, citing a 1937 warning by the founder of modern China, Mao Zedong.

"Still today, political liberalism floats up from the dregs from time to time," the paper added.

The "fundamental reason the military constantly moves from victory to victory is the strict maintenance of political discipline and preserving the Party's leadership", it added.

China's military, the world's largest, has made similar warnings in the past, including in April when it ordered its forces to be on guard against "liberalism" in order to avoid and purge internal corruption.

China's forces have been shaken by Xi's war against deep-seated corruption, which has toppled some of the military's most senior officers.

China stepped up a crackdown on corruption in the military in the late 1990s, banning the People's Liberation Army from engaging in business. But the military has been involved in commercial dealings in recent years due to a lack of checks and balances, military analysts have said.

Anti-graft advocates say corruption in the military is so pervasive that it could undermine China's ability to wage war.

(Reporting by Paul Carsten; Editing by Ben Blanchard & Kim Coghill)