Austrians will decide on Sunday whether to maintain compulsory military service or switch to a professional army in a referendum that has split the small, neutral country.

The cost of a reformed army, the number of recruits it can expect to sign up and the impact this will have on foreign missions and disaster relief have been the subject of heated debate for months, along with the fundamental question: what would this mean for Austrian neutrality?

"The nature of the threat has changed, that's why a transformation is necessary," Defence Minister Norbert Darabos, who is pushing for a more efficient and specialised army, said at a military ceremony last year.

A conventional army was outdated in an era of "counter-terrorism, cybercrime... (and) failed states," the Social Democrat added in a political talk show over the weekend.

The army's chief of staff, General Edmund Entacher, has warned however that a professional army would lead "irreversibly to a drop in quality, numbers and ability".

Austria is one of just a handful of EU countries to retain conscription, along with non-EU members Switzerland and Norway. Several states made the move towards a professional army only in the last decade, the latest example being Austria's neighbour Germany in 2011.

Critics of reform fear that doing away with the obligatory military service will push Austria to join NATO -- something it has repeatedly refused in the past -- and endanger the country's staunchly defended neutrality.

Austria's army currently counts some 55,000 troops, and this will remain unchanged, the defence ministry insists.

However, a replacement will have to be found for those soldiers who reported every year for national service duty: some 11,000 men for every six-month stint, or 22,000 in total.

Critics -- including top generals and the Social Democrats' coalition partner in government, the conservative People's Party (OeVP) -- have also warned of the added expense of setting up a professional force, with Interior Minister Johanna Mikl-Leitner equating it to a "two-billion-euro ($2.7-billion) castle in the sky".

Others argue a reduced force will not be able to respond to disasters as quickly and efficiently, or participate in foreign missions as it does now.

Austria is proud of its long-standing involvement in UN peacekeeping missions, especially in the former Yugoslavia and the Middle East.

The army has otherwise been mobilised mostly at home to deal with disaster situations like floods or avalanches.

Conscription proponents have predicted horror scenarios if conscientious objectors are no longer available to help key social services and emergency teams, leaving them without much needed staff. Every year, some 14,000 men opt for a nine-month community service stint instead of military service.

The issue has split the government right down the middle, with the People's Party backing the status quo -- supported by the far-right Freedom Party -- while the Social Democrats, Greens and two smaller parliamentary parties want a professional force.

Whatever the outcome of the referendum, reforms are in store for the army, although details are still scarce from both the Social Democrats and conservatives.

This will be Austria's first ever nationwide referendum, and although not binding, the government has vowed to respect the result.

The latest opinion polls predict that voters will prefer to maintain conscription by about a 10-point margin.

But the number of undecideds and of people who have said they will not vote is high, pollsters noted, with Darabos hoping for just 40-percent participation in a country where turnout in general elections usually hovers around 80 percent.

"The parties' tedious squabbling over the army seems to have left a considerable number of Austrians confused and disinterested," the Spectra polling institute commented.

Some 6.3 million Austrians are eligible to vote on Sunday, with preliminary results expected within hours of the polls closing at 5:00 pm (1600 GMT).