WASHINGTON (REUTERS) - Neil Gorsuch, President Donald Trump's US Supreme Court nominee, on Monday emphasised the need for judicial independence even as Trump castigates jurists who have ruled against him, while Democrats questioned whether he would rule against abortion rights and gun control while favouring corporations.

With the ideological balance of the Supreme Court at stake, the Senate Judiciary Committee opened its confirmation hearing for Gorsuch, a conservative federal appeals court judge from Colorado.

Republicans praised Gorsuch, 49, as highly qualified for a lifetime appointment as a justice.

"I think we're off to a good start," Republican Chuck Grassley, the committee's chairman, said afterward, with senators getting their first shot at questioning Gorsuch on Tuesday.

Committee Democrats noted Gorsuch has the chance to join the court only because Senate Republicans last year refused to consider Democratic former President Barack Obama's nomination of federal appellate judge Merrick Garland.

Despite slim chances of blocking his nomination in the Republican-led Senate, Democrats raised questions about Gorsuch's suitability for the job.

"Our job is to determine whether Judge Gorsuch is a reasonable, mainstream conservative or is he not," said the panel's top Democrat, Dianne Feinstein.

Speaking publicly for the first time since Trump nominated him on Jan 31, Gorsuch defended his judicial record in the face of Democratic criticism of his rulings.

Gorsuch, speaking mostly in generalities that could not cause him any trouble, emphasised the need for "neutral and independent judges to apply the law", warned against judicial overreach, and referred to "the modest station we judges are meant to occupy in a democracy".

"If judges were just secret legislators, declaring not what the law is but what they would like it to be, the very idea of a government by the people and for the people would be at risk,"Gorsuch said in comments in harmony with conservative criticism of unelected "activist judges".

Gorsuch, a cool-headed and amiable jurist, gave Democrats very little ammunition to use against him, although there could be more drama when he takes questions. The hearing could last four days, providing classic Washington political theatre.

Grassley said the panel is likely to vote on the nomination on April 3, with the full Senate vote likely soon after.

If Gorsuch is confirmed by the Senate, as expected, he would restore a narrow 5-4 conservative court majority. The seat has been vacant for 13 months, since the death of conservative Justice Antonin Scalia in February 2016.

Democratic Senator Richard Blumenthal underscored the importance of judicial independence at a time when Trump has excoriated federal judges who have ruled against him on matters including two executive orders, put on hold by courts, to block people from several Muslim-majority nations from entering the United States.

Blumenthal said it was not "idle speculation" to suggest the Supreme Court might be asked to enforce a subpoena against Trump, citing FBI Director James Comey's testimony before Congress on Monday confirming an ongoing investigation into alleged collusion between Trump's presidential campaign and Russia.

Republican Ted Cruz said there is no reason for Gorsuch to be questioned about Trump, noting that previous nominees have not had to speak about allegations made against the president who nominated them.

Democrats highlighted cases on which Gorsuch has ruled and questioned the influence of conservative interest groups in advising Trump on his selection.

Feinstein emphasised abortion. Conservatives have long opposed the landmark 1973 Roe v Wade ruling legalising abortion nationwide. Feinstein called that ruling and others since then buttressing abortion rights "super precedents" deserving special deference.

Feinstein cited two Gorsuch legal opinions in which she said he "argued in favour of making it harder to convict felons who possess guns".

Democratic Senator Patrick Leahy said he was worried that Gorsuch's conservative method of interpreting the Constitution"goes beyond being a philosophy and becomes an agenda" that is anti-abortion, anti-environment and pro-business.

"Will you allow the government to intrude on Americans'personal privacy and freedoms? Will you elevate the rights of corporations over those of real people? Will you rubberstamp a president whose administration has asserted that executive power is not subject to judicial review?" Leahy said.

Many Democrats contend Trump's party "stole" a Supreme Court seat by freezing out Garland. "Your nomination is part of a Republican strategy to capture our judicial branch of government," Senator Dick Durbin told Gorsuch. "That is why the Senate Republicans kept this Supreme Court seat vacant for more than a year and why they left 30 judicial nominees who had received bipartisan approval of this committee to die on the Senate calendar as President Obama left office."

Gorsuch said he has tried to treat all who come to court fairly and with respect. "I have decided cases for Native Americans seeking to protect tribal lands, for class actions like one that ensured compensation for victims of nuclear waste pollution by corporations in Colorado," he said. He also said he has ruled for disabled students, prisoners and workers alleging civil rights violations, and for immigrants who entered the country illegally.

The court's ideological leaning could help determine the outcome of cases involving the death penalty, abortion, gun control, environmental regulations, transgender rights, voting rights, immigration, religious liberty, presidential powers and more.

Republicans hold 52 of the Senate's 100 seats. Under present rules, Gorsuch would need 60 votes to secure confirmation. If Gorsuch cannot muster 60, Republicans could change the rules to allow confirmation by a simple majority.