The pension measures would save at least 4 billion euros a year as well as fulfill European Union policy recommendations issued in May which senior euro zone sources said were being used as a blueprint for the terms of a sovereign aid program.

The accelerated raising of the retirement age to 67 from 65, currently scheduled to take place over 15 years, is a done deal, the sources said. The elimination of an inflation-linked annual pension hike is still being considered.

Spain is hesitating to apply for external aid to handle a high public deficit and soaring debt. Its borrowing costs fell on Thursday at an auction of a 10-year benchmark bond but relief may be short-lived.

The new pensions steps, which could be announced as soon as next week along with the 2013 budget, would send a strong signal to investors that Spain is serious about implementing structural reforms it has delayed because of the political cost.

Prime Minister Mariano Rajoy, who was forced earlier this year to break campaign pledges such as not raising taxes, has repeatedly said he would not touch pensions, but he has few options left to trim the budget after drastic cost cuts.

He toned down his language last week and said it would be "the last thing" he would do.

Deputy Prime Minister Soraya Saenz de Santamaria on Friday denied the government was studying stopping periodic pension rises.

"The prime minister has said publicly that the first thing he did when taking power was bring pensions up to date and that should be respected ... in his exact words, it would be the last thing he would touch," she told reporters after a weekly cabinet meeting.

Sources with knowledge of the government's thinking said Rajoy's comments were a sign that his stance was shifting.

"He just said that he would not cut the pensions. But did you hear anything else? We both know that there are several ways of cutting. One is to simply leave them steady against inflation," said one of the sources.

A second source said the acceleration in the change in the retirement age was backed by the government while a third source, who discussed the issue with senior Spanish officials, said a freeze was expected.

"Not increasing them is also an adjustment," the third source said.

FREEZE

Many economists also believe a freeze is inevitable.

The 2012 budget earmarks a rise in pension spending of 3.2 percent, including a 1 percent inflation-linked review, but inflation is running close to 3 percent, meaning an extra 4 billion euros would be paid to pensioners in January but booked to the 2012 budget.

So cancelling this year's inflation-linked raise would save the government between 5 and 6 billion euros.

For following years, based on annual inflation of 2 percent, the reference used by the European Central Bank to set its main rates, the adjustment would cost 4 billion euros.

"There is no way around it. You have to cut the link with inflation and freeze the pensions next year," said Jose Carlos Diez, chief economist at Intermoney brokerage in Madrid.

"And to me, that would be just a start... The pensions, the unemployment benefits and the borrowing costs are eating up all the efforts on the spending side so you need to act in those areas," he added.

Both removing the inflation adjustment and accelerating the retirement age increase are long-standing European Union demands and any bond-buying program to help Spain finance its debt would insist on this, senior euro zone sources said.

Countries which were previously rescued, such as Greece, Ireland and Portugal all had to pass steep cuts on pensions.

In Greece, the cuts ranged from 20 percent to 40 percent, while new pensioners had a 10 percent pay cut in Ireland and Portugal scrapped the Christmas and summer extra payments.

SUSTAINABILITY

While an announcement could be made next week when the government adopts the first draft of the 2013 budget, political analysts say Rajoy may be tempted to wait until after a regional election in his native Galicia.

The timing of any request for European aid is in Rajoy's hands. Some pointers suggest he could make the move along with the budget package to pre-empt a credit review by ratings agency Moody's, due by end-September, which might otherwise downgrade Spanish debt to junk status. Moody's has said it would welcome a Spanish aid request.

However in Brussels, EU officials close to the discussion said they did not expect Madrid to seek an assistance program before the October 21 regional vote. That would mean Spain would have to get over a 30 billion euro refinancing hump at the end of October, including 9 billion euros in short-term paper, without the euro zone rescue fund or the ECB buying its bonds.

The spread between Spanish and German benchmark 10-year bonds, a measurement of the perceived risk of investing in Spain, widened a few basis points on Friday to 417.

As Reuters reported first last month, Spanish officials led by Economy Minister Luis de Guindos have been talking discreetly to the European Commission since at least early August about possible conditions and supervision for a precautionary program that would keep Spain in the capital markets.

De Guindos made clear at a meeting of euro zone finance ministers in Cyprus last weekend that Spain, keen to avoid having terms imposed from outside, would announce its own reform measures and timetable on September 28, a day after a draft 2013 budget is approved by the cabinet.

Rajoy performed especially well among pensioners when he was elected in a landslide last year and his first move after taking office was to restore the inflation adjustment his predecessor Jose Luis Rodriguez Zapatero had removed in May 2010 because of the euro zone debt crisis.

Zapatero also passed a law last year to add two years to the retirement age by 2027. Rajoy's People's party, then in the opposition, voted against the change.

With unemployment soon to top 25 percent and set to remain at high levels until at least 2015, the number of people contributing to the state pension system has fallen to its lowest in 10 years. There are now 2.39 workers supporting one pensioner.

The government tapped 4.4 billion euros from an insurance fund to make July and August payments to the 8.1. million pensioners, about a fifth of the population.

It also said it could not rule out using the pension guarantee fund -- meant only for emergencies -- by the end of the year to pay the pensioners their monthly cheque.

(Additional reporting by Luke Baker and Paul Taylor in Brussels; Editing by Fiona Ortiz, Philippa Fletcher, Paul Taylor and Giles Elgood)