Soviets announce tentative agreement on reactor inspection.

Twin announcements here and in Moscow Thursday suggest a hopeful wisp of straw may just possibly be blowing in the high wind now buffeting East-West relations.

A spokesman for the Vienna-based International Atomic Energy Agency (IAEA) here disclosed that the Soviet Union has agreed - after two years of talks - to open its civil nuclear reactors to the agency's international inspection process.

In Moscow, the official Soviet news agency Tass said that IAEA and the Soviet Union have ''harmonized the preliminary basis'' of a draft agreement on the relevant safeguards.

The disclosure was made on the eve of the international agency's annual meeting, which is to be held here next week. It may have been made with an eye to the meeting of the UN General Assembly this week.

IAEA's board of governors are to meet during next week's conference. But the draft is not expected to be on its agenda before early 1985.

With this agreement, the Russians have at last followed the American and British example in voluntarily submitting their civilian nuclear reactors to agency inspections devised to ensure that nuclear fuel is not diverted to military uses.

Voluntary agreement is in line with the international nuclear Non-Proliferation Treaty. Under that treaty, nonnuclear signatories are obliged to accept inspection but the nuclear powers themselves are not. They are, however, urged to submit voluntarily to IAEA supervision.

European diplomats and other international observers are not reading too much into this Soviet gesture.

Thursday's announcement, therefore, is also being read in conjunction with statements by Soviet Foreign Minister Andrei Gromyko in his Sept. 19 talk with David Rockefeller, former chairman of the Chase Manhatten Bank. While continuing (pro forma) to hold the US primarily responsible for the present cold war, Mr. Gromyko was at pains to insist that the Soviet Union desires ''fair and serious'' talks with the Americans.

There is still widespread conjecture over the motivation of the Russians' move a few weeks ago to initiate the Gromyko visit to the White House. East European diplomats and other officials seem to know little more about it than their counterparts in the West.

Since Gromyko agreed to a Sept. 28 meeting with President Reagan, the East Europeans have said virtually nothing of the issues - except for hard-line echoes from Prague and Warsaw of Moscow's attacks on West German ''revanchists.''

Almost the only comment from more moderate quarters came Thursday in two of Budapest's principal newspapers. Magyar Hirlap spoke, probably more optimistically than most, of ''looking forward with great expectations'' to the coming White House meeting.

Nepszabadsag, the Hungarian party newspaper, appealed to the General Assembly to take the opportunity to make a ''major contribution'' to a better international atmosphere and to promote a ''substantial dialogue'' in East-West relations - and above all, a ''normalization'' of US-Soviet relations.

The East Europeans seem to be taking the position that the Gromyko-Reagan meeting could be the last chance for some time to make a dent in the deadlock between the superpowers.

''Things have reached a point much worse than so many people in the West appear to think,'' a highly placed and influential East European journalist said in recent private conversation. ''They seem not to be aware how precarious this situation has become. That is the most serious and the most worrying thing.''