WASHINGTON (REUTERS) - Texas Senator Ted Cruz, a conservative firebrand who frequently clashes with leaders of his Republican Party, will become the first major figure from either party to jump into the 2016 U.S. presidential election race on Monday.

Cruz is expected to announce his candidacy at Liberty University, an evangelical Christian school in Virginia, according to an aide, giving the Tea Party favourite a head start on what is likely to be a crowded field of Republican White House contenders.

Cruz, 44, has built a reputation as an unyielding advocate for conservative principles in his two years in the Senate. As a presidential candidate, he is likely to portray himself as the most reliable proponent of small government.

"We need to look to people who walk the walk and don't just talk the talk," he told the Conservative Political Action Conference in February.

More than a dozen potential presidential candidates are already courting donors and voters in states like Iowa and New Hampshire that vote early in next year's primary season. But none are expected to enter the race formally until April at the earliest, in order to maximize their advantage under campaign finance laws.

As the lone official candidate, Cruz will get extra attention from the media and voters for several weeks.

But once he has declared his candidacy, his political operation will face more legal restrictions. He will have to file a fundraising report in mid-April, for example, while others will not have to disclose their finances until mid-July.

While non-declared candidates like former Florida governor Jeb Bush can solicit million-dollar checks for their political organisations, Cruz will not be able to ask supporters for more than US$5,400 (S$6,205), the maximum contribution allowed for candidates.

The Canadian-born son of a Cuban immigrant, Cruz, would be the first Hispanic in the White House if he won the November 2016 election.

In his time in the Senate, he has sometimes drawn the scorn of senior Republicans. Arizona Senator John McCain, the 2008 Republican presidential nominee, famously called him and other Tea Party lawmakers "wacko birds" in 2013.

Later that year, Cruz pushed his party to force a 16-day government shutdown in an unsuccessful effort to deny funding to President Barack Obama's healthcare law, the Affordable Care Act. He led a similar effort this year, also unsuccessful, to block Obama's effort to remove the threat of deportation for some undocumented immigrants.

Despite - or perhaps because of - his unpopularity in Washington, Cruz's appeal among grassroots activists has grown.

In recent weeks, he has criticized other potential Republican candidates for supporting comprehensive immigration reform and the Common Core educational standards. He has called for abolishing the tax-collecting Internal Revenue Service and stationing its agents on the U.S.-Mexico border.

Cruz is a proven fundraiser, collecting in US$18 million for his Senate race and raising another US$2 million to distribute to other candidates, according to the Centre for Responsive Politics.

He will aim to raise between US$40 million and US$50 million over the course of the Republican primary campaign, according to the Houston Chronicle.

That might be less than the total raised by more establishment-friendly candidates like Bush or Florida Senator Marco Rubio, who is viewed favourably by many wealthy donors in a conservative network led by billionaire industrialists Charles and David Koch.

Cruz is currently supported by 8 per cent of self-identified Republicans in a Reuters/Ipsos tracking poll. Bush leads the poll at 21 per cent, and Wisconsin Governor Scott Walker ranks second at 16 percent.

Several other potential candidates are statistically tied with Cruz, including Rubio, Kentucky Senator Rand Paul, New Jersey Governor Chris Christie, former Arkansas Governor Mike Huckabee, and retired neurosurgeon Ben Carson.

The Democratic field is shaping up to be far leaner. Former secretary of state Hillary Clinton has yet to declare her candidacy, but is currently viewed as the front-runner in her party.