UPDATE 1-Argentina's Pecom says 90 pct accept bond swap

(Updates with background paragraphs 4-7)

BUENOS AIRES, Argentina, June 27 (Reuters) - Argentina's Pecom Energia said on Thursday that 90 percent of its bondholders had agreed to a bond swap offer aimed at helping the country's No. 1 energy firm through a crippling recession.

The main unit of holding company Perez Companc said in a statement it would extend its offer of up-front cash to July 3 for those who participate in its attempt to swap about $997.5 million in old debt for new issues that extend maturities by three years.

Pecom hopes the swap, which combined with a renegotiation of bank debt aims to restructure about $2 billion in debt, will allow it to avoid default amid Argentina's four-year recession that has virtually cut off credit to local companies.

The final deadline for the swap is July 9. Since the offer was announced on June 10, Pecom has declined to speculate on what will happen to bondholders who do not participate, though most analysts expect the deal to be successful.

If successful, Pecom's would be the biggest corporate debt restructuring in Argentine history and possibly set it apart from other local firms such as Telecom Argentina and steel company Acindar that have suspended debt payments.

However, HSBC Bank Argentina said last Friday it had rejected a debt payment originally due in dollars but Pecom made in devalued pesos. Pecom said an Argentine law switching dollar debts into pesos at parity made the payment valid.

Pecom has about $2.3 billion in total debt, including $1 billion due this year alone, and has had to indefinitely suspend its plan to shift cash flow toward oil production after several years concentrated on exploration.