Premier Romano Prodi was struggling to maintain unity in his centre-left coalition on Monday as a rift deepened over possible plans to enlarge a US base at the northern city of Vicenza.
The project, which would create the biggest American military base outside the US, is firmly opposed by left-wing and pacifist elements in Prodi's disparate, nine-party coalition.
But several other parties, including the centrist, Catholic UDC and the Radicals, are equally convinced it should go ahead to prevent damage to Italo-US relations.
Vicenza's centre-right city council approved the project in a narrow vote last October but the final word rests with the seven-month-old government, in particular Prodi and Defence Minister Arturo Parisi.
The US has demanded that Italy decide by the end of this week.
Vicenza hosts an American military base with 2,600 troops. The expansion project would involve building barracks at Vicenza's airport Dal Molin to accommodate 2,400 more US troops who are currently stationed in Germany.
If the government nixes the plan, the old base would be shut down and American troops transferred to Germany.
The centrist Parisi has spoken in favor of the base's expansion, arguing that it is in the spirit of friendship between Italy and the US and would be a natural extension of the current US military presence in Vicenza.
Justice Minister Clemente Mastella, who heads the tiny centrist UDEUR party, also argued on Monday that Italy had to "respect its international commitments".
"If Italy refuses to enlarge the base, the Americans would regard it as a slap in the face, not aimed at (US President George W.) Bush but at their country. It would affect our relations with the US as a whole and not just its government," the minister said.
Radicals chief Daniele Capezzone said rejecting the base's expansion would be a "serious mistake" because it would harm ties with the US, and be "self damaging" because it would lead to the loss of hundreds of local jobs.
But the Democratic Left (DS), the largest government party, and others including the Greens, the Communist Refoundation Party (PRC) and the Italian Communists' Party (PDCI) renewed their protests on Monday.
The DS underscored surveys showing that 70% of Vicenza residents are against enlarging the base.
The PRC, the third largest party in government, said that a green light would imply "incomprehensible support for the disastrous policies of the Bush administration" and would be a continuation of the foreign policies of the previous government headed by Silvio Berlusconi.
The Greens argued that the project would have a "terrible impact" on the surrounding urban environment.
Other critics said Vicenza citizens should be allowed to decide for themselves via a referendum.
Vicenza's council has thrown out proposals to hold a referendum on the base's fate even though local polls have shown that 84% of citizens would like to have a say on the issue.
There have been repeated demonstrations by local residents against the base expansion plan.
But there have also been smaller protests by those who argue that Vicenza's economy will suffer if the base is closed and that more than 1,200 locals who currently work at the base will lose their jobs.
Meanwhile, the centre-right opposition led by Berlusconi accused the Prodi government of "anti-Americanism" and said its stance was "jeopardising relations between Italy and the US".
Prodi has so far avoided commenting on the issue.
A defence ministry statement issued last week said that the government had not yet reached a "conclusive decision" because it "cannot just ignore the objections and doubts raised by a large part of the local community".
