Add elements of whodunit to the controversy surrounding the full-page advertisement by "Concerned Americans for Peace" published in The Post and four other large newspapers July 11. The ad excoriated an "insensitive" Israel for waging "a senseless war" in Lebanon, attributing to "press reports" 40,000 killed or wounded and 700,000 homeless.

If "Concerned Americans for Peace" existed when the space here and in the New York Times, Chicago Tribune, Atlanta Journal and Constitution and Los Angeles Times was purchased--at approximately $25,000 a page--there's no evidence it does now. Los Angeles postal authorities say the return address in The Post--P.O. Box 5305, Terminal Annex--is bogus. Then, the agency which placed the ad, Hodes Advertising of Los Angeles, has said cryptically that an employee, Pat Howard, "was used." By whom, as if that weren't important, no one will say.

Agency president Bernard Hodes told Post reporter Joanne Omang earlier this week the ad was "placed out of channels," that he is "furious" with his employee and that he doesn't know "who's behind this." A report that the ad was placed on behalf of another California agency--Copley, Lane and Capen--has been denied to me by Paul Copley, the firm's president.

Repeated efforts to learn more from Mr. Hodes or Mr. Howard have been fruitless. Telephone inquiries are not answered, including at Doyle Dane Bernbach, a large New York agency of which Hodes is a division, and which clearly is avoiding any notion of responsibility. All we have, as a result, are footprints and suspicions, not the least of which is that the ad was covertly funded by the Palestine Liberation Organization.

The controversy arose, as Joanne Omang reported, when the American Friends Service Committee, American Red Cross, CARE, Save the Children Federation, U.S. Committee for UNICEF and Church World Services-- listed as channels for assistance to Lebanon--disavowed any association with the ad. The Post published a letter from them July 16.

The Los Angeles Times, as a result of checking beforehand, ran the ad without the organizations' names. The Christian Science Monitor refused to accept it, said advertising director Clayton Westland, owing to the disavowals and because "we were uneasy about where the money was coming from and couldn't get clear answers." Mr. Westland was told three individuals represented "Concerned Americans for Peace," but all were "out of the country." The Chicago Tribune reported being given the names of Ralph Martin, vice president, and John Kelly, secretary treasurer. I could obtain no confirmation of these names.

In accepting the ad, Post advertising staff followed its established procedures. First, it received a customary "insertion order" from Hodes. The agency has been known reputably in the trade as a "recruitment" advertiser, i.e. listing "professional opportunities." This was followed by a standard industry form from the sponsor, certifying that the relief groups had given permission to be listed. Apart from its illegible signature, the document misled all newspapers. The cashier's check drawn on the Mitsui Manufactuers Bank, Encino, Calif., for payment here provides no other clue to "Concerned Americans for Peace."

In a review of the ad's content, The Post questioned the casualty figures. They were adjusted downward by Mr. Howard, presumed at the time to be speaking for Hodes, to levels reported in the June 28 Newsweek. Thus, The Post ad read, "News reports have placed the number of people killed and wounded at over 26,000 with . . . homeless a staggering 600,000." The other papers ran the higher numbers as submitted.

Noting the differences, the Jewish Community Council of Greater Washington asked whether The Post associated itself with these "terribly inflated figures." It does not; nor does it with the ad's anti-Israeli rhetoric. The paper similarly questioned statements and figures in a 28-page supplement, "Life in Israel," which it carried last month. Even though alterations were agreed to by A. S. Epstein, of Beverly Hills, Calif., the supplement, which ran in only 100,000 copies of the paper, evoked some stong criticism. To be sure, in that case the paper knew precisely with whom it was dealing. In the current one, as it turns out, there was deception.

While defending its procedures, Post advertising department officer Charles Hollingsworth said its certification requirement will be more vigorously examined. He points out the paper acted on the word of an established advertiser with whom it had done trustworthy business for years. The Post presumed that Hodes, in turn, was being dealt with honorably by something called "Concerned Americans for Peace." This paper and others now know that was not so. Which is easier to say than "whodunit."