By Patricia Zengerle

WASHINGTON, May 25 (Reuters) - Obama administration officials told U.S. lawmakers on Wednesday they would oppose new sanctions on Iran if they interfere with last year's international nuclear agreement, laying the groundwork for a potential fight over any legislation.

"If legislation were to undermine the deal, by taking off the table commitments that we had put on the table, that would be a problem," Adam Szubin, the acting Treasury Department Under Secretary for Terrorism and Financial Intelligence, told a House of Representatives Foreign Affairs Committee hearing.

Members of both the House and Senate are drafting new sanctions measures. They accuse Iran of supporting terrorism, human rights abuses and violating its international commitments by testing ballistic missiles.

"I feel it's not so terrible to have Congress come up with new sanctions if we feel Iran is violating its agreements," said Representative Eliot Engel, the committee's top Democrat, who opposed the nuclear deal announced in July 2015.

Every Republican in Congress and several of President Barack Obama's fellow Democrats opposed the nuclear agreement. But the deal's backers could not muster enough support to override Obama's promised veto of legislation stopping the deal, and it went ahead.

Szubin and Stephen Mull, the State Department's lead coordinator for implementing the nuclear deal, said that, so far, the deal is being fully implemented.

"We believe that we and our allies in the region are considerably safer," Mull said.

Members of Congress recently have accused the administration of allowing sanctions workarounds that might provide Iran direct or indirect access to the U.S. financial system or allow it to use the dollar in some transactions.*:nL2N17L14Z

Szubin reiterated the administration's assurances that it has no such plans. "Iran will not have access to our financial system," he said.

Despite the easing of nuclear sanctions under the international agreement, Iran's hopes of rapidly ending its economic isolation have been complicated by the concerns of companies that doing business with Iran might violate non-nuclear sanctions that remain in place.

(Reporting by Patricia Zengerle; Editing by Chizu Nomiyama) ((, ; 001-202-898-8390; Reuters Messaging: