President Clinton lay a wreath at the Tomb of the Unknown Soldier this morning before setting off for Moscow to join inV-E Day celebrationswithRussian President Boris Yeltsinas a prelude to a two-day summit. Their agenda will include such sensitive subjects as Chechnya, NATO's plans for expanding its membership and Moscow's nuclear deal with Iran. At ceremonies in Arlington, Va. this morning markingNazi Germany's World War II surrender, the president mixed conciliatory comments on U.S.-Russian relations with denunciations of "the tragic war" in Chechnya and Moscow's plans to sell nuclear technology and material to Iran. As he departed, the White House officially issued his executive order imposing a full trade ban on Iran, a nation he called the "principal sponsor of global terrorism." Even the trade ban hasn't satisfied Republicans leaders: Sunday, Senate Majority Leader Bob Dole and House Speaker Newt Gingrich both threatened to cut U.S. aid to Russia if Yeltsin goes through with the Iran deal. Administration officials said they expect Clinton to use those warnings -- and some classified information about Iran's nuclear program -- to pressure Yeltsin when the summit begins tomorrow.