You are excused if you were confused by various headlines in various newspapers after President Reagan's mini press conference April 14. The Post's front- page headline read "President Admits Aiding Guerrillas Against Nicaragua." That's not what the man said.

Others, relying on an Associated Press account, said "Reagan Denies U.S. Backs Rebels" or "U.S. Denies Aiding Rebels in Nicaragua." The New York Times had "Reagan Says U.S. Is Acting Legally Over Nicaragua"; The Baltimore Sun, "U.S. Policy Backed on Nicaragua," and The Wall Street Journal, "Reagan Denies U.S. Trying to Topple Nicaraguan Regime With Arms to Rebels."

Questions arose after members of Congress expressed concern that the administration is violating a law prohibiting assistance to anyone aiming to overthrow the Nicaraguan government. Mr. Reagan denied this, but several times sidestepped specific questions about direct aid to the "contra revolutionaries." The closest he came was: "Anything we're doing in that area is simply trying to interdict the supply lines which are supplying the guerrillas in El Salvador." Hence, the more accurate Post headline on an inside page: "Reagan Acknowledges Aiding Guerrillas for Benefit of El Salvador."

There can be little question that the "contras" are receiving covert assistance. Insurgent spokesmen have said as much in interviews. Still, with the limited exception cited above, the administration has refused to discuss the matter publicly. Maybe Mr. Reagan will clear all this up when he addresses a joint session of Congress tonight.

New old subject:

A story last December from Beirut by Loren Jenkins, who shares this year's Pulitzer Prize with New York Times correspondent Thomas L. Friedman for coverage of the war in Lebanon, has been faulted by some for advancing questionable data. Jewish Week, among other critics, charged The Post with "rewriting history."

Mr. Jenkins wrote that prior to the U.N. vote partitioning the land governed under the British Mandate, Palestine had 1.3 million Arabs and about 600,000 Jews; Arabs owned 93 percent of the land, and the U.N. vote gave 53 percent of the territory for the new state of Israel.

Jewish Week and others asserted that 8.6 percent of the land was owned by Jews, 3.3 percent by Arabs and 16.9 percent "was abandoned by Arabs." The remainder, "more than 70 percent," the paper said, "was government territory that had belonged not to Arabs but to the Turkish Empire." The figures were attributed to "outgoing British administrators who cannot be regarded as pro- Jewish or pro-Israel."

Other official figures--the Palestine Government's Village Statistics, April 1945--showed Jews owning 5.6 percent; a U.N. document of November 1947 puts the figure at 6.8 percent, which included land in Jewish possession but not legally owned. It appears indisputable that Jews had been prevented from buying land since 1939. The highest figure, according to various other sources, places Jewish ownership at 6.8 percent.

It may be that critics address their data, as Jewish Week wrote, to "the land that made up the state of Israel in 1948," whereas Mr. Jenkins was looking at all the territory. His figure of 93 percent ownership by Arabs is a compilation of 47.77, again according to the Village Statistics Act and other sources, plus 46 percent where the inhabitants were almost exclusively Arabs. In addition to his own knowledge, Mr. Jenkins said recently that he relied for background on three different British authors who have written extensively on the period. Perhaps "ownership" was too precise a term for the remaining 46 percent and may not have been "deeded" land.

Others criticized Mr. Jenkins' statement that 700,000 Arabs "fled into a new diaspora" after partition. Jewish Week says that "Israel also insists . . . that many Palestinians responded to appeals from fellow Arabs. . . ." Among those who refute the Israeli contention are Erskine Childers, whose "The Other Exodus" observes, "Examining every official Israeli statement about the Arab exodus, I was struck . . . that no primary evidence of evacuation was ever produced." And Howard M. Sachar in "History of Israel": "There were various reasons for this flight, but none of them could be traced to an alleged appeal for evacuation by Arab governments. This was a frequently repeated Israeli claim after the war. No such order for evacuation was ever found. . . ."