It began as an ambitious multibillion-dollar plan to give Brazil a brand-new air force to suit its status as an aspiring regional power but nearly eight years on, the acquisition program has hit more delays.

A $4.5 billion plan to buy 36 fighter jets for the air force will not be considered until later this year but the air force will go ahead with retiring its aged fleet of about a dozen Mirage 2000 warplanes, officials said. The Mirage aircraft are now considered too expensive to upgrade and are likely to be sent back to France as they cannot be resold.

Brazil bought the used jet fighters from French manufacturer Dassault in 2005, when it also announced plans to buy 36 new fighter jets. Acquisition plans at the time called for purchase of "next generation" fighter jets but defense aviation technology has moved on.

The government initiated a competition. Three advanced fighter jets -- Boeing's F-18 Super Hornet, Rafale from French manufacturer Dassault and Gripen NG from Sweden's Saab are vying for the contract, said to be worth at least $4.5 billion in inventory, maintenance and training costs.

Brazil is also having to rethink state spending priorities amid nationwide protests over what critics call a mismatch between national need and official outlays. Protesters from nearly all walks of life want the government of President Dilma Rousseff to spend more on basic infrastructure, shun grandiose projects and reduce income disparities.

Brazil is hosting the soccer World Cup next year and the summer Olympics in 2016.

This month the government announced ambitious plans to invite private sector participants to infrastructural development, sparking more controversy from critics including workers of state enterprises, who fear privatization by the back door.

Controversies over government spending have pushed back air force modernization, and it's far from certain if the latest postponement of the FX-2 competition to December for Brazil's fighter purchase will be the last.

But with no decision likely any time soon on the FX-2 program the air force is looking at options as the entire Mirage fleet reaches end of its operational life.

The Mirage 2000 fleet, stationed at a base near Brasilia, will be retired by the end of the year, O Estado de Sao Paulo daily reported. It's not clear if the FX-2 purchase will be decided, as widely expected, before the Mirages stop flying.

Critics called the purchase program so far piecemeal and potentially harmful to the Brazilian air force's overall strategy.

Earlier this year Brazilian aircraft manufacturer Embraer said it would modernize more of the country's ageing Northrop F-5E fighters and F-model trainers.

Embraer is also upgrading more than 40 of AMX light-attack aircraft, adding new avionics likely to be compatible across the military's fleet.

Saab received a Brazilian air force order for upgrading its Erieye Airborne Early Warning and Control Mission System. Critics say the air force needs a more integrated and comprehensive strategy for modernization.