China's top automaker SAIC Motor Corp has reached out to General Motors Co GM.UL to explore the prospect of taking a stake in the automaker when it goes public this fall, four people with knowledge of the matter said.

The contact between state-backed SAIC -- which has a 13-year relationship with GM -- and GM has been informal and the expression of interest by the Chinese automaker could hit a quick dead-end if the U.S. government objects to the move, several of the sources said.

In its informal contact with GM, SAIC has expressed an interest in acquiring a single digit share in GM, one person with knowledge of the discussion said.

Because the SAIC contact with GM remains private and preparations for GM's IPO are covered by strict U.S. securities regulations regarding disclosure, none of the sources agreed to be named.

A spokesman for the U.S. Treasury declined to comment on discussions about who might buy shares in the IPO, but the Treasury late on Friday clarified for the first time the rules that will be applied to the GM IPO.

In an online posting the Treasury said that the IPO would be open to a wide range of investors including overseas funds and U.S. retail buyers.

A GM spokesman could not be reached for comment but GM has repeatedly declined to comment on the IPO, citing securities regulations.

GM and its advisers also are making appointments to meet with sovereign wealth funds over the next few weeks to sound out their interest in committing to buy and hold major stakes as so-called cornerstone investors, one of the sources said.

U.S. officials have taken a cautious approach to foreign investor participation in the GM IPO because of the prospect for any such investment to trigger a political backlash.

As of earlier this month, the U.S. Treasury had not yet decided how to handle the question of potential stakes in GM by sovereign wealth funds, a move that would help create demand among other investors, one of the sources said.

The government pumped $49.5 billion of taxpayer money into GM in a still-controversial bailout that kept the automaker from liquidation but earned the nickname Government Motors from critics.

Ahead of November congressional elections, the Obama administration has been working to convince voters that the 2009 rescue packages for GM and Chrysler spared the auto industry an even more wrenching downturn.

(Reporting by Kevin Krolicki in Detroit, Clare Baldwin in New York, Fang Yan in Beijing, Soyoung Kim in New York and Philipp Halstrick in Frankfurt; editing by Carol Bishopric)