Libya's senior diplomat have repeated yesterday that a cutoff of oil exports to the United States is only an option that will be studied by his government in the aftermath of the Reagan administration's decision to shut the Libyan Embassy. The United States cited "provocations and misconduct" by Libya, "including support for international terrorism," in expelling its diplomats.

Hours before his departure, Ali Houderi reaffirmed for reporters what he had said several times since the announcement of his expulsion: that he was not making any threats to actually cut off the oil flow nor was he sure that such action would be chosen by Col. Mummar Qaddafi's government in Tripoli.

Houderi, who left the United States shortly after midnight with 26 other diplomats and about 50 family members, spoke without bitterness and with a generally conciliatory tone during a news conference. Flanked by large photographs of Qaddafi, Houderi said his country wanted good relations with the United States and was "optimistic" about resolving difficulties. He expressed the hope that current problems could be settled quickly and that the downgrading in diplomatic relations would be short-lived.

Libya is the third largest exporter of oil to the United States, and supplies a special type of so-called "sweet" crude that is more easily refined into gasoline and is used by many East Coast refineries. The United States buys about half of Libya's oil, Houderi claimed, in return for which Libya receives about $12 billion a year.

State Department and White House officials have said they see no reason why the diplomatic action should interrupt this business relationship. These officials believe that Qaddafi does not want more of a confrontation with the United States now, and that he needs the U.S. money to finance his arms buildup and various foreign military adventures, including paying for mercenaries in his army.

In addition, there is now a glut in world oil supplies, so other buyers of Libya's oil could be hard to find. U.S. specialists also believe it would be hard to keep track of where the oil goes even if Qaddafi attempts to embargo the United States.

Houderi acknowledged yesterday that there was a "they-need-us-and-we-need-them" aspect to the oil situation and that Libya did need U.S. oil company expertise. But he argued that "our dignity and pride, to a certain extent, are more important than selling oil to a place we don't feel comfortable to deal with," and added that "if we have to use our oil to protect our interests, we will."

Houderi rejected the oil-glut argument, saying that the special brand of Libyan crude "can't be replaced overnight or even in months." He said Libya could sell more oil in Europe or use it in its own petrochemical industry if necessary. He said Libya's decision would be based on its self-interests and would not be an emotional one.

Though the United States has publicly and privately accused the Libyans of involvement in terrorism, the administration has not made public any specific details underlying the decision to expel the Libyans. Last year, eight Libyan exiles living in Europe and opposed to the Qaddafi regime were murdered; a Libyan student dissident was shot and wounded in Colorado last fall.

U.S. officials say privately that there are strong indications that the Colorado shooting is linked to a Qaddafi-ordered campaign to silence critics abroad; these officials say they wanted the Libyans out of this country before an assassination attempt here was successful.

Houderi denies any Libyan involvement in the Colorado incident. He said he has challenged the State Department to back up its allegations and has received no detailed response.

The State Department is able to expel diplomats broadly charged with misconduct. But expulsion of other Libyans here requires legal proceedings.

About 4,000 Libyan students remain in this country. Since Libya will no longer have diplomatic representation here, even via a third country, Houderi announced that the remaining Libyans had formed a five-member "people's committee," with no official status, that will informally handle the affairs of the remaining Libyans and constitute a "symbolic" effort to keep the door open.

Asked about reports of a big Libyan loan to Nicaragua after the United States cut off aid to its leftist revolutionary government, Houderi said he was not well-informed about that situation but that in general his country had no apologies to make for such actions.

Asked about reports of Soviet-built Libyan missiles being moved to Syria in the confrontation with Israel, Houderi again said he was not in a position to comment but that his government fully supports Syria "and will use Libyan forces if we have to to defend and liberate all Arab land."