BUENOS AIRES, Jan 25 (Reuters) - Argentine President Javier Milei's "omnibus" bill, a sprawling reform package ranging from tax hikes to privatizations, has cleared its first hurdle in Congress with a green light from a lower house committee. It now faces far tougher obstacles.

The bill, part of a major push to reshape the South American country's embattled economy, will require majority approval from lawmakers in both chambers of Congress, where Milei's own libertarian coalition only holds a small minority of seats.

It is a key plank of Milei's reform plans since taking office last month, aimed at reviving the fortunes of South America's no. 2 economy, which is battling inflation over 200%, high poverty levels and crippling public debt.

As part of the bill, the government would privatize a raft of public firms - though it has backtracked on selling off state energy firm YPF - and introduce a broad 15% tax on most exports, with top export soy and its derivatives rising to 33% from 31%.

The lengthy legislation faces a debate in the lower chamber of deputies next week, with some conservative and moderate blocs in Congress supportive, though often with conditions, while more left-leaning lawmakers are generally opposed.

Milei's right-wing coalition has only 15% of the seats in the lower house and 10% in the Senate, but he has allied with the main conservative bloc and brought a range of political voices into his government.

"Many of us have the will to accompany the government and help it in the necessary reforms to get the country out of this crisis," Radical Civic Union lawmaker Martin Tetaz said, according to a read-out of the lower house committee debate.

"But we are convinced that these reforms cannot be done at the expense of austerity on retirees, cannot include increases in taxes on production and, much less, on exports."

The official Peronist bloc, the main opposition, was more forthright in their plans to try to knock down the bill.

"As a bloc we are going to express our rejection," said the head of the Union por la Patria coalition German Martinez, adding he expected other political parties to join them.

"It is a very serious mistake to give more powers to this president, who wants to trample over everything," Martinez said.

Deputy Santiago Santurio from Milei's La Libertad Avanza bloc said the bill would "rebuild" Argentina. "It's a process to leave behind the decadence that politics has left us in and begin a growth project led by the people," he said.

The bill, which goes hand in hand with an equally broad presidential decree, has faced opposition from various fronts, including against the planned tax hikes, deregulation that could impact the environment and spending cuts to the arts.

Far-left lawmaker Myriam Bregman argued strongly against the bill, which she said looked like it was written by business lobbies and the International Monetary Fund (IMF), with which Argentina has a shaky $44 billion loan program.

"La Libertad Avanza does not have the numbers to approve this nonsense, they can only do it because there are those who collaborate with the disaster to which they want to lead our country," Bregman said.

(Reporting by Adam Jourdan Editing by Bill Berkrot)