If he weren't slowed by an illness, Rep. Morris Udall, the Arizona Democrat and former presidential candidate, might have taken to the House floor to dance in the aisle. President Reagan, in his Nov. 21 summit report to a joint session of Congress, singled out an idea that Udall and other internationalists have been long pushing.

Reagan, reversing his position, promised "to go forward with a number of people-to- people initiatives that will go beyond greater contact not only between the political leaders of our two countries but our respective students, teachers and others as well. We have emphasized youth exchanges. They will help break down stereotypes, build friendship and, frankly, provide an alternative to propaganda."

Udall, though not bowled over, did have to lean on his sturdy sense of humor to keep upright. The Reagan administration has consistently opposed as useless Udall's U.S.-Soviet Student Exchange for Peace bill. In 1983, when the legislation had 141 cosponsors in the House, a Reagan administration official testified that although such a bill has an "idealistic intent," it "could not be successfully implemented, or have a significant effect in reducing tensions."

The conversion of the administration reminded Udall "of an old Henry Fountain Ashurst story. That great statesman, concerned about Franklin Roosevelt's attempts at packing the Supreme Court, introduced legislation designed to block Roosevelt. Ashurst received so much flack for his proposal that he ended up leading the fight to defeat his own bill. A constituent wrote him a letter congratulating him for his noble stand on the Supreme Court issue. Ashurst replied by telegram, 'Which one?'

Udall now says to Reagan: "Mr. President, I congratulate you on your stand on the value of U.S.-Soviet exchanges -- and I'm referring to your latest stand."

In his office the day after the Reagan speech, Udall spoke of welcoming the newcomer Reagan to the cause. The bill itself, which calls for an annual exchange of 2,000 young people from each country for a period of one year, was reintroduced earlier this year. Sen. Paul Simon (D-Ill.) has sponsored it in the Senate.

"The length of the exchange," Udall explains, "is important. All too often, two-and three-week exchanges become vacations. A one-year period wil allow students to study the language, culture and societal attitudes in depth. The best way to destroy deeply ingrained U.S. and Soviet stereotypes is by giving young people an opportunity to live in the other country."

Americans have a near bottomless ignorance about Russian life, culture and thinking. The State Department reports that "in the area of Soviet foreign policy, the number of doctoral dissertations defended in American universities in recent years is minuscule. In 1974-79 the average number was eight, and less than six when dissertations by foreign students were eliminated." In the 1970s, enrollment in Russian-language courses in U.S. colleges fell by one-third. A 1982 study found that 1,660 professionals in Russian studies were needed by governmental, academic and private firms, but that only 1,074 of the jobs were filled.

Does it mean anything that Ronald Reagan has stopped ranting about the "evil empire," and now endorses youth exchanges? Mark Palmer, the State Department official who spoke against the Udall legislation in 1983, is still not endorsing it, even after Reagan's speech. He has questions about the largeness of the program -- 2,000 students -- and whether the Soviet government will agree to participate.

Those aren't fantasy problems. Udall's legislation would establish a commission to negotiate the details of the program with the Soviet government. With the Reagan administration's insatiable love of commissions, this approach ought to be a flag that earns an elbow-jerk salute. Udall and his office have been in contact with Soviet officials, and an understanding has been reached about a willingness to negotiate the specifics of an exchange program.

Udall hopes that the hate, fear and threats between the governments of America and Russia can come to an end. A man of innate goodness, he understands that goodness also exists in the Russian people. To recognize it, and learn more about it, is to accept reality.