Mikhail Gorbachev steamed into Washington 30 months ago with the force of a locomotive, casting a strong beam of light through the dark of the Cold War. This week the Soviet leader returns, resembling a flickering candle set at the edge of a gathering storm.

A sure sign that a leader is in serious trouble comes when he starts blaming his problems on the people. So it now is with Gorbachev. He gave his version of Jimmy Carter's "malaise" speech May 17, telling reporters that his economic reforms were failing because of the conservatism and apathy of the populace. True, perhaps; but the Russian translation of "malaise" must have sounded no more convincing or appealing to his people than did the original delivered in American Georgian.

Gorbachev's weekly pattern of marching up the hill of free market reforms on Monday and marching down by Friday has created a shambles that dwarfs the mess of Carter's "stop and go" approach to inflation (and to everything else). The Soviet leader must also now account for the unintended consequences of a foreign policy he has concocted a la James Earl: bold, idealistic and totally uncoordinated.

Weakness is the distinguishing characteristic of the 1990 Gorbachev, who arrives in Washington tomorrow. The Soviet leader has little choice but to try to convert calamity into bargaining strength at the summit with President Bush. Gorbachev arrives looking too weak to make more big concessions. Movement will have to come from Bush, particularly on the thorny issues of German unification and conventional arms control.

This time, the appearance of desperation is not an artifice adopted to entice concessions from President Bush or to consolidate the surprising sympathy Gorbachev receives from the American public in the extended showdown with the Lithuanians. Gorbachev looks vulnerable because he is vulnerable, at home and abroad.

"No one is for him any more," a leading Moscow intellectual and beneficiary of glasnost told me recently. "He will probably stay in place as leader because there is no clear alternative. But nobody is following where he is leading."

Moreover, Gorbachev's extraordinary foreign policy successes in changing the Soviet image abroad and in ending the Soviet war on Afghanistan are now tarnished by the serious miscalculation he made on Germany. He must try at the Washington summit to salvage something to pacify the simmering unease in the Soviet officer corps.

The unease was clearly expressed by the chief of the armed forces, Gen. Mikhail Moiseyev, with political commissars of the Soviet army two weeks ago. Intelligence reports on the meeting say Moiseyev took an unrelenting hard line, assuring the political officers that a united Germany would be demilitarized and neutral, and would host a Soviet military presence for a long time to come.

The tone, although not the details, is echoed in the most recent statements of Gorbachev and Foreign Minister Eduard Shevardnadze. Their concern about the generals will affect the summit as well. Gorbachev will probably try to get Bush to endorse a joint statement committing the superpowers to keep unification from affecting the military balance in Europe.

Bush will balk, not least because West Germany is urging him to avoid any statement that implies U.S. agreement with the Soviet view that special limitations need to be put on German armed forces. On this and other points, the president is in the happy position of being urged by his European allies to do exactly what he intends to do anyway at this summit.

That is, Bush will undoubtedly express sympathy for Gorbachev's plight, agree to work out limitations on a united Germany's troop strength but only as part of the NATO-Warsaw Pact talks in Vienna and stand firm on unfettered German membership in NATO.

A year ago Europeans would have been pushing Bush to "help" Gorbachev. But the tone is also changing in the West. Senior European officials and diplomats speak less today of helping Gorbachev and more of pursuing policies that will keep the Soviet Union actively engaged with the West through the storm ahead.

Unspoken but clear in such statements is the sense that it is important to plan for dealing with the Soviets in a post-Gorbachev era, should that become necessary. His fate is no longer the key question; the fate of the Soviet Union as a nation state is.

Gorbachev must face not only the generals when he gets back from Washington but also a vital Communist Party congress, set to last a marathon 10 days. He may also confront a popular referendum on the latest half-way economic changes, which his government could easily lose. In the Soviet system, however, there is no mechanism in place to bring forward a Ronald Reagan to make everybody feel better about themselves and make it morning in Moscow again. More of the mess, or chaos, seem to be the choices.

Bush and his European allies have decided, rightly, that they cannot help Gorbachev past these tests by concessions for that purpose alone. This is one of those cases where the obvious solution is the best solution: the deals at the summit have to have mutual benefits for both sides that go beyond Gorbachev's immediate fate. This is how Bush will prevent Gorbachev's weakness turning into strength in Washington Summit II.