* Secretary of state called by prosecutors to testify

against onetime political ally

* David Rivera accused of acting as an unregistered agent

of Venezuela

* Rubio testifies he did not know about Rivera's contract

with Citgo

(Adds detail from testimony throughout)

By Luc Cohen

MIAMI, March 24 (Reuters) - U.S. Secretary of State

Marco Rubio testified on Tuesday that his longtime friend and

former U.S. Congressman David Rivera did not tell him that he

had a $50-million contract with a company owned by the

Venezuelan state when he took a meeting about Venezuela with

Rivera in 2017.

Rivera, 60, is standing trial on federal criminal charges of

acting as an unregistered agent of ousted Venezuelan President

Nicolas Maduro's government to try to ease U.S. pressure on the

country. Rivera has pleaded not guilty and his lawyers say he

was working to help the opposition get rid of Maduro.

Rubio's testimony has briefly taken him out of Washington, where

he has been engaged in high-level diplomacy around U.S.

President Donald Trump's war in Iran, and into the federal

courthouse in downtown Miami, his hometown and where his

political career began.

Rubio told jurors that Rivera, in a meeting in July 2017,

had told him that he was in touch with insiders in Venezuela who

had convinced Maduro to step aside.

Rubio said he was skeptical that the gambit would work, but

that he briefly told Trump the next day that "there might be

something happening in Venezuela," and that he would keep him

posted.

Under questioning by prosecutor Harold Shimkat, Rubio said

he was not aware that Rivera's company had been paid by U.S. oil

refiner Citgo Petroleum, a subsidiary of Venezuela's

state oil company.

Had he known, Rubio said, "I would have not taken any

subsequent action in this matter."

RIVERA SAYS HE TRIED TO HELP VENEZUELAN OPPOSITION

Rivera's defense lawyers are expected to cross-examine Rubio

later. Rivera represented South Florida in the U.S. House of

Representatives from 2011 to 2013.

Rubio testified that he and Rivera - both Cuban-American

Republicans and outspoken opponents of left-wing governments in

Cuba and Venezuela - were close friends and roommates earlier in

their political careers.

In his opening statement on Monday, defense lawyer Edward

Shohat said Rivera's interactions with Rubio were separate from

his contract with Citgo. He said Rivera's work for Citgo related

to business, not politics, and so he did not have to register as

a foreign agent.

"David Rivera had no reason to tell Rubio about that

contract," Shohat said.

Despite the alleged lobbying effort, Trump ramped up

financial sanctions on Venezuela during his first term.

MADURO CAPTURED IN JANUARY

U.S. special forces captured Maduro in a January 3 raid on

Caracas and brought him to New York to face drug trafficking

charges. He has pleaded not guilty.

Since Maduro's ouster, Venezuela has been led on an interim

basis by Delcy Rodriguez, and relations with Washington have

improved.

Jurors saw a Senate speech Rubio gave in 2017 in which he

said there was still a chance for a transition in Venezuela

without vengeance. Rubio said Rivera had told him that Maduro

government insiders feared retribution by the opposition if they

left power.

"Ironically, these words are very much aligned with what

we're trying to achieve now in Venezuela," Rubio said.