The eurozone's €440bn sovereign rescue fund will be operational by the end of the month and expects to be awarded a coveted triple A credit rating in August, its new head has said.

Spelling out details of how the European Financial Stability Facility would operate, Klaus Regling, chief executive, said: "We will be ready to act whenever the politicians tell us to act."

In an interview with the Financial Times, Mr Regling said the fund was a temporary crisis mechanism but could be extended beyond its intended three-year lifespan if any loans to eurozone governments were outstanding.

Many investors have doubted whether the fund would earn a triple A credit rating – a badge of credibility meaning it could borrow at the best possible rate. Only a minority of the eurozone members backing the fund have a triple A rating.

Mr Regling said specific measures had been taken to ensure the fund was awarded a top credit rating, including the build-up of a cash reserve and a guarantee by member countries to pay up to 20 per cent more than their agreed shares of the fund.

He said rating agencies had also been told there was a "general commitment from euro area countries to do whatever else is needed to get the best possible rating".

"I am confident that we will get the best possible rating, maybe some time in August," Mr Regling said. "I think the point that 16 finance ministers of mature economies promise to do whatever is necessary to get the best rating is worth a lot."

Eurozone governments agreed to set up the fund as the centrepiece of a €750bn "shock and awe" package to calm markets' concern about the mounting debts of several states including Portugal and Spain after the Greek debt crisis.

Governments will be able to borrow from the facility if they agree to adopt reform programmes designed by the International Monetary Fund, European Commission and European Central Bank.

They will pay a charge comparable to that levied on Greece when it was granted an emergency bail-out this year, Mr Regling said. "It does not mean there is an ATM machine. Everyone agrees that countries only get money when they accept conditionality."

With the results of stress tests on European banks set to be revealed next week, Mr Regling said the fund would not be used directly to shore up ailing banks, although governments drawing on the facility could use the money for bank recapitalisation.

Mr Regling, a former senior European Commission finance official, said yields on EFSF bonds would be "very similar" to those on German sovereign debt – considered a benchmark low-cost borrower – or multilateral development banks, such as the European Investment Bank.

Slovakia is the only eurozone member state not to have approved its support for the fund so far but Mr Regling and other EU officials have said they are not worried that this will delay the fund's operability.