MOSCOW, OCT. 23 -- The same thing happened this time last year.

The Americans came expecting a modest agreement that would lead to a summit in Washington. Then the Soviets raised the ante and the summit fell through, weighted down by the most contentious of arms control issues: President Reagan's strategic defense initiative (SDI) program.

Last year, it happened in Reykjavik, Iceland. This year's story is not over, but when Secretary of State George P. Shultz got on the plane here tonight, the prospects for an autumn visit by Soviet leader Mikhail Gorbachev to Washington were receding like the fog that had shrouded the Soviet capital all week.

Shultz left Moscow with almost everything but the summit dates. On the imminent treaty to eliminate medium- and shorter-range nuclear missiles, the two sides agreed on all but technicalities. On the more long-range issue of cuts in strategic or intercontinental-range offensive weapons, both sides were stressing compatibility. True, SDI remained a problem, but few here had expected it to hold up a summit scheduled for the signing of a treaty on the intermediate-range nuclear forces (INF).

So why did Moscow once again pull the rug out from under U.S. expectations? Had American expectations strayed from reality, egged on by innate optimism and internal political necessities?

The results of Shultz's two-day visit suggested another possibility: that Gorbachev had reduced his own expectations for a Washington summit because of objections raised within the Soviet establishment.

Answers to these questions hang on the tantalizing issue of whether a Washington summit has fallen off the political calendar for the rest of President Reagan's term.

A joint statement issued last month in Washington by Shultz and Soviet Foreign Minister Eduard Shevardnadze said that "in order to sign a treaty on intermediate-range and shorter-range missiles and to cover the full range of issues in the relationship between the two countries, a summit between President Reagan and General Secretary Gorbachev will take place. The summit will be held in the fall of 1987, with exact dates to be determined during talks between the secretary of state and the foreign minister in Moscow in October."

Today, this relatively unambiguous language seemed forgotten as the Soviet side insisted on "key provisions" for cutting strategic arms and strengthening the 1972 AntiBallistic Missile treaty. The latter is seen by Moscow as a bulwark against SDI, and as of tonight, the "main obstacle" to a summit.

"If we get the key provisions, then there will be no problem for a summit and the signing of a treaty on medium- and shorter-range missiles," Shevardnadze said at a press conference tonight. He reminded reporters that the Soviet side had always insisted that an INF treaty be accompanied by the "key provisions," ever since Shultz's last visit to Moscow in April, when the INF treaty became a real possibility.

Shevardnadze said the signing of an INF treaty does not depend on progress in the other two areas of arms control. "If there won't be an agreement on the key provisions, that does not mean that an agreement on INF will not be signed. But where and when is another matter."

This uncertainty over the venue of the fall summit did not arise for the first time tonight. Several western and Soviet analysts had noted last month that the joint statement pointedly failed to mention the site of the summit, even though it was widely assumed to be Washington.

In public and private statements, the Soviets stressed that the place of the summit was still under discussion. Various reasons were given for the deliberate vagueness: One, offered by a well-informed Soviet analyst last month, was that perhaps an INF treaty was not big enough to warrant a visit by the general secretary to Washington.

"Your side has been saying Washington. Our side has been ambiguous," the analyst said. Maybe, he said, a trip to Washington needed not just an INF treaty, but a "framework" agreement on other arms control issues similar to one reached in Vladivostok between President Ford and Soviet leader Leonid Brezhnev in 1975.

At the time, these Soviet hints were dismissed by U.S. spokesmen as last-minute bargaining by the Soviets. The Americans went further to say that if the summit did not take place in Washington, there would be no summit.

Protocol is on Washington's side. Since Brezhnev's visit to Washington in 1973, American presidents have paid two visits to the Soviet Union (Nixon in 1974 and Ford in 1975) and at Moscow's request, held three summit meetings in third countries (Carter in Austria and Reagan in Switzerland and Iceland).

If, as some western analysts hold, Moscow is using the summit as a bargaining chip, it is a shrewd assessment of Washington's deep interest in holding the meeting on American soil. According to one view, the summit is politically more valuable to Washington than the INF treaty itself. Therefore, in withholding agreement on the place and time of a third Reagan-Gorbachev meeting, Moscow is deliberately playing on Washington's weak point.

According to this view, Moscow this week simply played out its hand after raising expectations during the Shevardnadze visit to Washington in September. But if it is a bluff, it is not clear how Washington can call it -- particularly since Shultz today stressed again that the Reagan administration's commitment to SDI is not negotiable.

Some analysts here tonight argued that Moscow this week was not pursuing a grand strategy but executing an about-face, shifting suddenly from optimistic predictions of a Gorbachev tour of the United States to artful dodging on who would sign an INF treaty, when and where.

It is doubtful that Gorbachev received new signals on the summit from this week's unexpected meeting of the Communist Party Central Committee. Such foreign policy decisions here usually emerge from a consensus reached long ahead of time.

However, some analysts noted that the Shultz-Shevardnadze agreement in Washington on Sept. 18 was reached while Gorbachev was on vacation and was followed by a low-key reaction in the Soviet press. One western diplomat tonight noted that Gorbachev may have had reservations about whether an INF treaty was worth the propaganda show Washington seemed ready to stage over his visit to the United States.