BEIJING (Reuters) - China's military risks losing wars and bringing millennia of shame upon itself if it drags its heels on reform, the army's official newspaper said on Friday, warning that modernization of the armed forces was behind that of advanced foreign counterparts.

President Xi Jinping unveiled a broad-brush outline of the reforms last month, seeking further streamlining of the command structure of the world's largest armed forces, including job losses, to better enable it to win a modern war.

Xi is determined to modernize at the same time as China becomes more assertive in its territorial disputes in the East and South China Seas. China's navy is investing in submarines and aircraft carriers, while the air force is developing stealth fighters.

The reforms, kicked off in September with Xi's announcement he would cut service personnel by 300,000, have been controversial.

The military's newspaper has published a series of commentaries warning of opposition to the reforms and worries about lost jobs.

In a lengthy commentary provided by the Chongqing military command, the People's Liberation Army Daily said China had managed to narrow the gap with its peers in developed countries though existing reform programs.

"But, generally speaking, our military modernization level is not commensurate with the security needs of the world's largest developing country and the gap with the world's advanced militaries," it said.

China has too many levels of command, "backward" combat effectiveness and too many layers of bureaucracy, the paper said.

"This directly impacts upon and constrains our military in trying to raise the ability to win battles," it added.

History shows that only those who embrace change thrive, and "no change means falling behind and taking a beating", the commentary said.

"Looking at the situation broadly, whether the armed forces bring glory or disgrace ultimately rests on the basis of the country's power and military's strength," it added.

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"If there is no reform, once something happens and the armed forces cannot win, then they will be condemned through the ages."

There was no room for standing on the sidelines or prevarication, and those who spread "lies and slander" about the reform process must be firmly rejected, it added.

Xi's reforms include establishing a joint operational command structure by 2020 and rejigging existing military regions, as well as cutting troop numbers, to make the armed forces more streamlined and efficient.

On Monday, the same paper told high-ranking officers to hold their tongues about concerns over military reform and lead from the front to ensure the rank and file are on board.

(Reporting by Ben Blanchard; Editing by Nick Macfie)