Argentina and international bankers will meet next Tuesday to sign a $1.5 billion medium-term loan agreement that has been under negotiation since last September, Citibank Senior Vice President William R. Rhodes said yesterday.

Meanwhile, the International Monetary Fund has agreed to call an unusual August meeting of its Board of Executive Directors on Monday to review Argentina's policy and is likely to agree to allow the nation to draw the next installment of a $1.6 billion, 15-month loan, said Uvaldo Aguirre, the Argnentian official who has negotiated the bank loan.

The main obstacle to the loan signing has been financial sanctions between Britain and Argentina in the wake of the Falklands-Malvinas war last year. Earlier this week, Argentina announced that it would allow British firms in Argentina to repatriate dividends and profits. This cleared the way for the agreement by British banks to the medium-term loan.

Argentina owes about $40 billion overseas, and is the third-largest debtor in Latin America after Mexico and Brazil. Its loan arrangement with the IMF was dependent on the provision of new money from commercial banks. Rhodes said that the agreement between Argentina and its creditor banks was "a very positive step in the overall solution of the Latin American debt problems" and shows "that the people who have been saying for the last year that the system is going to collapse . . . were not correct."

Argentina received a $1.1 billion bridge loan from commercial banks early this year, and is asking banks to release the last $300 million of this so that it can make overdue interest payments for May. Rhodes said he hopes that this also will be settled next week.

Argentina still must agree with international bankers on the stretch-out of $6 billion of public-sector loans due to be repaid in 1982 and 1983 and $5 billion of private-sector loans from overseas, Aguirre said.