By Steve Scherer

ROME (Reuters) - Two of Italy's biggest unions marched through Rome on Friday to protest against Prime Minister Mario Monti's cuts in public spending as opposition grows to austerity policies aimed at steering the country out of its economic crisis.

The strike followed clashes between anti-austerity protesters and police in Madrid and Athens this week and coincided with labor unrest at the ILVA steel plant in southern Italy.

"We are here to protest against Monti's politics, because up until now he has just made the weakest pay," said Pio Zappaterreno as he rallied with fellow members of CGIL, Italy's largest union, in the city center.

Monti's coalition passed spending cuts in August that included a modest downsizing of the public sector, where wages have already been frozen for more than two years, and cuts to state healthcare funding.

University professors, public administration employees and health workers in the CGIL and UIL unions were to stop work in support of the march to the Colosseum. Garbage collectors were also joining the work stoppage.

"At the moment I just can't see a future that gives us any hope, particularly for the youth," former soldier Emilio Amiraglia said at the march.

The spending cuts followed unpopular austerity reforms and an overhaul of hiring-and-firing rules that drew stiff opposition and protests from labor unions earlier this year.

"Starve the beast, weaken it, make it inefficient, undermine its potential, interrupt its mission - these are the principles that are behind the government's public administration policy," CGIL's leaders wrote in a letter explaining the walkout.

To head off a Greek-style debt disaster, Monti raised taxes and cut pensions when he took over from Silvio Berlusconi in November, subjecting Italians to an "unprecedented amount of sacrifices," he said in an interview on CNN this week.

Austerity measures have hurt household spending and deepened Italy's recession. Italian unemployment rose to 10.7 percent in July, the highest since 2004.

Since August, anger over austerity and job losses has led to a growing number of industrial disputes, including at the ILVA steel mill in Taranto and at an aluminium smelter in Sardinia.

Although Monti is the most popular political figure in Italy, his comments on Thursday that he would be willing to serve again if no clear leader emerged from elections next spring prompted a chorus of complaints from opposition parties.

(Reporting by Steve Scherer; Editing by Giles Elgood and Jane Baird)