Historically, no group has been tougher on the duplicity and the sham of politicians than other politicians. Of Sir John Simon, who defected from his Liberal Party to sit among the Tories in the House of Commons, an angry David Lloyd George said: "The right honorable gentleman has for so long sat on the fence that iron has entered his soul."

It's too bad that Lloyd George couldn't have been around to hear either the speech Rep. David Obey (D- Wis.) gave to the Washington convention of the Arab-American Anti-Discrimination Committee this month or his speech in February to a San Franciso meeting of the National Jewish Community Relations Council. More important than the considerable content of the two speeches was their conscientious consistency. Obey, the chairman of the House Foreign Operations subcommittee with responsibility for foreign aid appropriations, delivered the same message to both groups while neither demonizing nor lionizing one side or the other.

To American Jewish audiences accustomed to a seemingly endless diet of Democratic and Republican officeholders who offer uncritical support for all Israeli leadership policies, Obey can be a real jolt. Examples: "It's in America's interests and in the interest of everyone who lives in the Middle East for the United States to have constructive relationships with other nations in the Middle East besides Israel, including Syria." "The large percentage of aid funds going to Israel and Egypt is not going to change so long as there is not peace in the area, because both parties have strong support in this country." "If further agreements are not reached to move beyond Camp David to address the legitimate interests of Jordan, Syria and the Palestinian people, that would be a tragedy. But I also think that Talmudic debates about who needs to move first are futile."

For anyone whose luck it has been to hang around the corners of American politics for a few hundred primaries and general elections, it is singularly refreshing to hear an American politician give a speech on the Middle East that does not endow the state of Israel with the capacity for infallibility or the curse of infidelity, most frequently the former.

To his Jewish-American audience, Obey criticized the inflexibility of the Syrians as well as the policies of Menachem Begin. To an Arab-American audience, Obey praised the enlightened leadership of Prime Minister Shimon Peres and criticized the inflexibility of the Syrians. A self- identified "friend of Israel," Obey argues that a friend and "an honest public servant must tell people not what they want to hear, but the truth."

In the judgment of former Common Cause president David Cohen, Obey's erstwhile collaborator on campaign spending reform and House ethics issues, Obey has been doing exactly that since his 1969 election to succeed Melvin Laird in the House. Cohen recalls Obey's calling him, full of anger, at what the congressman judged to be inexcusable Congress- bashing by Common Cause in its publications and statements.

Obey is no plaster saint. A fierce partisan, he is happy to remind his listeners -- at least those who are sympathetic to foreign aid -- that over the past 10 years, a majority of House Republicans, many of whom wax poetic about their love of Israel, have voted against the foreign aid bill. Obey is hot-tempered and has been known to sulk occasionally after a legislative setback. He can be quite prickly in close quarters, and his light touch has been compared to that of the relentlessly serious Ralph Nader. All in all, you'd probably choose to have him in your Congress rather than in your car pool. As one of the Capitol's most effective lobbyists puts it: "Obey is difficult, ornery, skillful and immensely courageous." But he's nobody's darling.

In an era when men run quite successfully for the presidency, the nation's highest political office, all the time protesting that they are not politicians, David Obey, not yet 47, is a political leader who will have no iron enter his soul from sitting on any fences. With an absence of self-righteousness, he manages to say what he means and to mean what he says. "When the crunch does come," as Obey sees it, "Israel will need advocates who are credible." Whether you agree with him or not, David Obey is clearly credible.