(Adds details on ways to boost IMF capital, byline)

By Walter Brandimarte

WASHINGTON, April 24 (Reuters) - Brazil, Russia, India and China agreed on Friday they would not commit capital to the International Monetary Fund until it develops flexible capitalization instruments that give them more power in the institution, Brazil's Finance Minister Guido Mantega said.

A long-awaited reform of IMF quotas is the final goal of the BRIC countries, but provisional instruments could be used in the short term to help increase the fund's firepower, as long as they satisfy the demands of emerging economies, according to Mantega.

"We, the BRIC countries, demand reforms at the IMF so we can be better represented," Mantega told reporters in Washington, after meeting the leaders of the other three countries.

"We will only talk about cash amounts after a new (capitalization) instrument is ready."

A possible instrument would be the issuance of a bond by the IMF. Mantega said the BRICs want a short-term bond, with liquidity in the secondary market, that could be added to the countries' foreign reserves.

"I suggested the bond to yield a little higher than U.S. Treasuries so we could reap some benefits when moving from Treasuries into those bonds," Mantega said, adding that one year would be a good maturity time for the bond.

The BRIC countries also demand part of the funds raised by the bond sale to be invested regionally, benefiting emerging countries in need of funds, Mantega said.