At the same time that Citigroup Inc was unsuccessfully trying to convince an arbitrator that the brokerage it owned with Morgan Stanley was worth as much as $23 billion, the U.S. Securities and Exchange Commission in August was asking Citigroup to document the valuation it had placed on the asset.

The request was made public on Friday when the agency posted written responses from Citigroup to questions from SEC staff about the bank's financial disclosures.

The SEC request was made in an August 22 letter, six days before the two companies announced they were extending the deadline to set the price that Morgan Stanley would pay for an additional 14 percent of the brokerage, of which Morgan Stanley already owned 51 percent.

At the time, the companies asked an arbitrator to set the price because they could not agree on the brokerage's worth.

Citigroup's valuation proved to be more than one-and-half times too high when the deal terms were finally stuck on September 11, and the company announced a $4.7 billion charge to earnings to write down the value on its balance sheet of its 49 percent stake.

After announcing the charge, Citigroup told the SEC it was submitting the requested valuation information in a separate letter, which was not released on Friday.

A Citigroup spokesman declined to comment on the correspondence with the SEC.

(Reporting by David Henry in New York; Editing by Leslie Adler)