By Jan Wolfe NEW YORK, June 7 (Reuters) - Former FBI Director James Comey's testimony that U.S. President Donald Trump expected loyalty and hoped Comey would drop an investigation of a former top aide could bolster obstruction of justice allegations against Trump, several legal experts said.

Such allegations might be used as the basis for impeachment proceedings, some of the analysts said. Any such step would face a steep hurdle, however, as it would require approval by the U.S. House of Representatives, which is controlled by Trump's fellow Republicans.

According to written testimony posted on the Senate Intelligence Committee's website on Wednesday, Comey said Trump told him during a one-on-one Feb. 14 conversation that former national security adviser Michael Flynn was a "good guy" and hoped that Comey could see his "way clear" to letting go a probe into ties between Flynn and Russia.

Trump had fired Flynn the previous day in a controversy over contacts between the retired general and the Russian ambassador to the United States.

Comey's account, released ahead of his appearance before the committee on Thursday, could show that Trump intended to impede the Flynn investigation, said Michael Gerhardt, a professor of constitutional law at the University of North Carolina School of Law.

"The express discussion of loyalty is disconcerting,” and could heighten speculation that the "president was trying to exert some pressure or at least exert some influence over the Russia investigation,” Gerhardt said.

Comey, who was fired by Trump on May 9, was leading an FBI investigation of Flynn as it looks into allegations of links between Russia and Trump's 2016 presidential campaign. Moscow and Trump have both denied any collusion.

Trump's lawyer, Marc Kasowitz, did not immediately respond to a Reuters query about whether Comey's testimony would support an obstruction case. But he said in a statement that Trump felt "vindicated" by Comey's confirmation he was not under investigation in any Russia probe.

QUESTION OF INTENT To build a criminal obstruction of justice case, federal law requires prosecutors to show that a person acted with "corrupt" intent. It does not matter whether the person succeeds in impeding an investigation.

While a sitting president is unlikely to face criminal prosecution, obstruction of justice could form the basis for impeachment.

Bruce Green, a professor at Fordham University School of Law, said it would be difficult to show Trump intended to impede the Flynn investigation. He said Trump could say he was merely vouching for Flynn's character and voicing concerns about how the probe was interfering with his ability to function as president.