WASHINGTON (AP) _ Radio Marti, the U.S. government station that broadcasts news to Cuba, reassigned its White House correspondent Thursday for violating an agency policy by questioning President Reagan at his news conference Wednesday night.

Voice of America director Richard W. Carlson said the reporter, Annette Lopez-Munos, broke a rule dictated by U.S. Information Agency Director Charles Z. Wick that reporters who work for VOA and its station to Cuba, Radio Marti, not seek to question the president at formal news conferences.

USIA is the parent agency for the radio operations.

Appearing on the Cable News Network, Miss Lopez-Munos said she was unaware of the rule.

Carlson told reporters at a news conference that she had been reminded of the prohibition on Tuesday. And the president of the White House Correspondents Association said Miss Lopez-Munos had asked the group to reverse the policy.

Presidential spokesman Larry Speakes said: ''Our rule is that, as far as the White House is concerned, all briefings and all press conferences are open to all legitimate news organizations and we have no bar against anyone asking questions.''

White House deputy press secretary Dan Howard said, ''The White House has no set policy with regard to whether or not U.S. government news people may ask questions at presidential press conferences.''

''That is a matter for the government agency concerned to decide,'' Howard added.

At the news conference, Miss Lopez-Munos asked Reagan:

''Mr. President, there has been an obvious change in policy towards Iran - from refusing to deal with a terrorist state, to even sending weapons as a gesture of good will. Would you consider, in the name of the same geopolitical interest that you invoked in Iran, changing your policy towards Nicaragua?''

Reagan answered that ''we still hold to our position, and Iran officially is still on our list of nations that have been supporting terrorism.''

Miss Lopez-Munos then asked a second question:

''Then, Mr. President, would you consider breaking diplomatic relations with Nicaragua to increase the pressure on the Sandinista government?''

Reagan said that step was not under consideration and proceeded to explain his reasons for supporting the cause of the Contras battling the leftist Sandinista government. The president added that he believed ''there is a value in maintaining relations. It gives us a listening post in Nicaragua.''

VOA's Carlson told a news conference Thursday: ''As government employees ... we are careful to avoid situations that could lay us open to charges of favoritism or improper questioning.''

''The reporter in question had been reminded of this policy two days ago,'' he said.

''I have no problem with the question itself,'' Carlson added. ''It has to do with the fact that she asked the question at all and the unprofessional way in which she asked it. She seemed ill-prepared. She asked it without ever looking up. She did not really do well by Radio Marti in her appearance.''

Carlson said VOA reporters are allowed to ask questions in all other circumstances including of the president in less formal situations.

Wick ''does not want to give even the appearance of softball questions,'' Carlson said.

Radio Marti went on the air May 20, 1985, under orders from Congress to maintain balance in in its news reports.

Although President Reagan initially proposed the service as a propaganda broadcast, Congress insisted on putting it under the supervision of the Voice of America which, by charter, maintains objectivity.

The legislation directed the staff to provide ''news, commentary, and other information about events in Cuba and elsewhere to promote the cause of freedom in Cuba.

An official of the National Security Council denied reports that the NSC had objected to Miss Lopez-Munos' questions.

'The National Security Council has never expressed an objection to Miss Lopez-Munos' query, nor to any other question asked by a reporter at a press conference,'' said the official, who declined to be identified.

Carlson also denied NSC involvement in the squabble.

In her CNN appearance, Miss Lopez-Munos said she was told by a supervisor that the White House had raised the issue with her superiors.

She did not return calls to her home or the CNN studios. She told CNN she did not go to work today because she had a cold.

Miss Lopez-Munos had sought reversal of her agency's policy and had asked the White House Correspondents Association to reverse a policy enunciated in 1974 that held it was inappropriate for government employees to question the president as reporters.

CBS News White House Correspondent Bill Plante, association president, said the group informed her supervisor on June 10 that ''members of the current board ... have unanimously agreed that it should not be the role of the White House Correspondents Association to decide which accredited reporters may ask questions. We believe this should be a matter determined by the agencies and subject to White House policy.''

The association functions primarily as a dinner committee, is not elected by the journalists who cover the White House and does not participate in accrediting White House reporters.