WASHINGTON — Republican presidential hopeful Mitt Romney vowed Thursday to dramatically cut government spending and forgo tax hikes if elected, pinning his fiscal politics firmly to his party's conservative base.

Ticking off a series of cuts long relished by the right, the former Massachusetts governor vowed to cut federal spending by $500 billion in 2016.

"Washington is full of sacred cows that supposedly can't be slaughtered and electrified third rails that allegedly can't be touched," Romney wrote in a USA Today opinion article.

"As president, I will bring to Washington the turnaround philosophy it so badly needs."

Romney promised to cut government posts, slash funding for the arts, public broadcasting, family planning and passenger rail services, while giving states more budget power and launching a "stem-to-stern" review of government departments.

Promising to "eliminate every government program that is not absolutely essential," he also vowed to keep defense spending intact while keeping tax hikes "off the table."

Romney also renewed a promise to repeal President Barack Obama's health care reforms, a measure that Romney claimed would save $95 billion in 2016.

The reforms have been incendiary issue for Romney, who introduced a similar plan in Massachusetts while governor, but now distances himself from it.

"By the end of my first term, I will bring federal spending as a share of GDP down from last year's staggering 24.3 percent to 20 percent or below," he wrote.

"With the downgrade of America's credit rating, we've gotten a taste of that bitter reality as we see the full potential of fiscal disaster playing out across Europe. We must turn around while we can."

Romney hopes the budget plan, set to be unveiled in full Friday, firms up his conservative credentials as he rallies to motivate the party's grassroots.

In most national polls, Romney trails conservative darling Herman Cain in the race for the nomination, despite Cain being embroiled in multiple allegations of sexual assault.

According to Gallup pollsters, Romney is seen with less enthusiasm by Republicans and Republican-leaning independents.

Romney's plan is being unveiled as the debate over cutting the massive US deficit rages in Washington.

A bipartisan Congressional "super committee" is struggling to reach a deal on $1.2 trillion worth of cuts in time for a November 23 deadline.

If the deadline is missed, a series of automatic and draconian cuts will enter into force.