A MASS TURNOVER in the leadership brings communist China's movement away from its once rigid Marxism to renewed Western attention. At one stroke, the leading patron of reform, Deng Xiaoping, staged the exit of 10 Politburo members and 64 members of the Central Committee. Most are near the 81-year-old Deng's age and will be replaced by technocrats who can ensure the continuity of his country's "second revolution." To measure the scope of the shuffle, recall that another putative Marxist reformer, the Kremlin's Mikhail Gorbachev, has removed only one Politburo member. Deng Xiaoping is serious.

What he is first of all serious about is modernizing China. Seizing power 36 years ago in a desperately poor country, China's communists applied Marxism in the Stalinist command-from-the-top mode then dominant and found it abysmally wanting. Mao Tse-tung turned to a brutal low-budget model called the Cultural Revolution: another disaster. Phase 3 now finds old warhorse Deng attempting an immense intellectual and political breakthrough to a "socialism" that relies heavily on material incentives, a market economy and an open door to world capital and technology.

The West looks on agog. It's not simply China's size and Mr. Deng's audacity -- can you believe the Shanghai stock market may reopen? A communist country's turn at least in the direction of the capitalist road is ideologically satisfying. A political adversary's turn toward a system that would strengthen its common interests with the United States is a geopolitical boon. It is much easier for Americans to indulge their longtime admiration of China's people and culture when China is moving this way.

The road, to be sure, is long. Many party bureaucrats shrink from a change that will shift power to economic managers. Ideologues and traditionalists fear the undermining of established dogma and structure. The military worry about budget: early demobilization of a quarter of the 4-million-man standing army is due. A historic sensitivity to foreign "exploitation" helps explain some of the lingering coolness to foreign investors. And the inefficiencies of the current system do, after all, spread the available work around.

In the Soviet Union, Mr. Gorbachev chases crooks, tightens work-place discipline and cuts down national drinking. He likes the word renewal, but what he's renewing is tight, central authority. For a socialist system, real reform means letting economic power flow from the center toward, if not fully to, the people. This is the fateful course China is on.