The Communist Party of the Philippines (CPP), which rejected a Christmas ceasefire with the government after peace talks collapsed, also said seizing power remained its ultimate goal.
In a statement issued on the eve of its 37th anniversary, the CPP said it had ordered its 8000-member New People's Army (NPA) to "intensify guerrilla warfare on a nationwide scale".
In September, Arroyo was politically weakened after the communists rebuffed her peace offer.
Arroyo, however, overcame an impeachment vote in parliament, arising from opposition allegations that she cheated her way to victory in the presidential election in 2004.
Rumours of a coup plot by military and police officers swept the capital earlier this month and a retired general was arrested on sedition charges.
Entering an alliance
Arroyo overcame an impeach-
ment vote in parliament
The CPP central committee said: "At the appropriate time, the party would be willing to openly enter an alliance that includes the anti-Arroyo military and police forces not only for the purpose of ousting the Arroyo regime but also for the purpose of resuming the peace negotiations."
The rebels said they were approaching the final year of a three-year plan to build up the weaponry and fighting skills of the NPA, which the statement said now "operates in more than 100 guerrilla fronts" in most of the country's 79 provinces.
Raids and ambushes by the rebels forced government troops "to take defensive positions and divide [their] forces by guarding [their] own fixed positions, supply and transport lines, vital installations, depots and enterprises".
The central committee said it the NPA would shortly achieve armed parity with the military.
The CPP, however, said that if the opposition succeeded in overthrowing Arroyo, it "would be willing to resume the peace negotiations with the [new government] and to propose truce and alliance for the purpose of confronting the three evils of foreign monopoly, capitalism, domestic feudalism, and bureaucrat capitalism".