By Tom Westbrook

SYDNEY (Reuters) - Australia has urged legislators to take a more cautious approach in backing China's pursuit of "legitimate interests" and stay alert to the motives guiding its investments, in a briefing book published by the non-partisan parliamentary library.

Authored by government officials and distributed ahead of Tuesday's opening of parliament, the booklet raises concerns that "creating a Eurasia-wide, China-led bloc to counter the United States" is the long-term aim of China's "One Belt, One Road" project, including its investments in northern Australia.

"Some see this initiative as a profound challenge to the current global political and economic status quo," a parliamentary library researcher wrote in the book, designed to guide lawmakers on issues likely to come before them.

"Australia needs to adopt a more economically and strategically prudent attitude in determining how the Australia-China economic relationship is to further develop."

The caution comes after Treasurer Scott Morrison this month blocked the sale of electricity network Ausgrid to China and Hong Kong buyers, citing undefined national security concerns.

That followed his rejection of a Chinese consortium's bid for Australia's largest pastoral holding, S. Kidman & Co.

The 205-page briefing book is being handed out to members of parliament ahead of the first session after the July 2 election.

China is Australia's largest trading partner and a large source of foreign investment, spending $11.1 billion on Australian assets, mostly property, in 2015, accounting and advisory firm KPMG and the University of Sydney have said.

However, a decision to lease a commercial and military port in northern Australia to a Chinese firm last year raised concerns in the United States.

The parliamentary booklet sets out China's "broader uses" for its growing economic influence.

"China's rise and pursuit of its 'legitimate interests' have been supported by successive Australian governments," it said.

"A key question emerging from China's recent actions in the South China Sea is where do these 'legitimate interests' begin and end — do they include the establishment of 'spheres of influence'?"

(Reporting by Tom Westbrook; Editing by Clarence Fernandez)