(Updates with peso open, background on Letes payment postponement, country risk)
By Walter Bianchi and Cassandra Garrison
BUENOS AIRES, Dec 20 (Reuters) - Argentina's peso currency opened slightly weaker on Friday, traders said, after a decree stating the government would postpone payments on some short-term debt notes and a sweeping bill of economic measures was expected to move to the Senate.
The peso opened 0.29% lower at 59.99 per U.S. dollar, traders said, after the government said it would postpone the payments on short-term debt known as "Letes" until Aug. 31, 2020. Argentina's country risk rose 21 basis points to 1,950, the JP Morgan Emerging Markets Bond Index Plus showed.
About $9 billion in "Letes" payments due to expire from Friday would be impacted, according to a government source, as the new administration of President Alberto Fernandez inherits a mounting economic crisis and prepares to renegotiate about $100 billion in debt with bondholders and other creditors including the International Monetary Fund (IMF).
Letes held by people or provinces would be exempt from the decree, the source said.
In August, the government of former President Mauricio Macri announced it wanted to extend maturities of short-term debt, and would negotiate new time periods for loans to be paid back to the IMF for its $57-billion financing package with Argentina.
"The re-profiling of the notes had already been considered by investors," said Gustavo Ber, an economist at local firm Estudio Ber.
Meanwhile, Argentina's lower House passed an economic plan proposed by the government earlier on Friday which includes an array of tax hikes on grains exports, personal property and foreign assets held abroad.
With 134 votes in favor of the bill 110 against, the center-left government obtained enough support for its "Social Solidarity and Production Reactivation" project to move to the Senate, where it could go to vote later on Friday.
Fernandez's economic bill, the cornerstone of his governing program, aims to maintain fiscal balance to guarantee the future payment of public debt - currently under renegotiation - and, at the same time, expand social spending to boost the economy as Argentina struggles with annual inflation over 50%, higher poverty and higher unemployment.
"We want to convey to those who are part of the domestic market, that this is a tool to start the economy and give them hope," Sergio Massa, a member of Congress who is a Fernandez ally, said on Twitter. (Reporting by Walter Bianchi, Cassandra Garrison, Eliana Raszewski and Nicolas Misculin; Editing by Alison Williams)