A CIA covert action plan that upset a congressional committee, combined with a mixup in the press about which country was the plan's target, has caused a headache for the Reagan administration and for the government of Mauritania.

Informed sources say the actual target of the proposed CIA action was Mauritius, an island in the Indian Ocean off the southeast coast of Africa, not Mauritania, a large country on the northwest coast of Africa.

These sources say the plan involving Mauritius did not involve cloak-and-dagger action but was mainly a quiet CIA effort to slip money to the government there to help counteract financial aid being supplied to forces opposing the government by Libya's radical ruler, Muammar Qaddafi.

The episode began to unfold publicly July 25 when The Washington Post reported that the House Select Committee on Intelligence, in a highly unusual move, had written to President Reagan objecting to a planned secret CIA operation in Africa.

The stories' sources did not disclose what country was involved. The White House and the committee confirmed that such a letter had been written.

The next day, advance copies of Newsweek magazine's Aug. 3 issue reported that the committee had objected to a large-scale, multiphase operation to overthrow Qaddafi, with the ultimate goal of removing him from power, a description which to some implied assassination. The White House denied the Newsweek report.

Then on July 28, a Washington Post story, attributed to administration officials, said the operation was planned against Mauritania, not Libya.

Hours after that story appeared, "the Mauritanians, justifiably, went up the wall," one informant says, and demanded explanations at the State Department and from U.S. officials in their country.

At first, U.S. officials tried to tell Mauritania that they could not discuss alleged or real covert actions; then they tried to convince them that the press account was wrong. One source says the United States still is not sure the Mauritanians believe the explanation.

This source says the designation in the press of Mauritania probably came about because of confusion in the names of the two countries, both of which are relatively obscure to Americans.

On Aug. 4, The Wall Street Journal wrote it correctly, but not many people noticed. Amid a story about the then forthcoming visit of Egyptian President Anwar Sadat, the Journal noted that the "administration's concern about Mr. Qaddafi is so great that key congressmen have been briefed on a covert U.S. operation planned to check Libyan influence in Mauritius, an island in the Indian Ocean that the U.S. feared could become a Soviet naval base."

Still, the overt battle over covert activities continued. In its Aug. 10 edition, Time magazine called Newsweek's account of the plot against Qaddafi "misinformation" leaked to Newsweek as part of a "false report" being spread by "CIA sources," apparently to discredit CIA Director William J. Casey and then director of operations Max Hugel.

Time said that "CIA sources" also were spreading the "deceptive" leak about Mauritania but that the actual plan that drew congressional objection was a much broader CIA action to shore up U.S. interests in the Middle East and North Africa.

In its Aug. 10 edition, Newsweek said the "schemes" against Libya had been discussed with the House committee but reported committee confusion about whether the protest letter involved Libya or another controversial operation in the Third World.

Several sources have suggested privately that there clearly is widespread interest within the administration and the intelligence community in complicating Qaddafi's life and that various plans have been discussed. These sources suggest that they do not involve covert U.S. actions against Qaddafi inside Libya.