During this past week the diplomatic world expected United States President Reagan to be firm with Israeli Prime Minister Menachem Begin and tell him to stop the killing in Lebanon. No such thing happened.
Mr. Begin was sharply criticized on Capitol Hill in Washington, but not at the White House. In Lebanon, Israeli troops launched new forward operations while Mr. Begin was at the White House.
Three weeks ago at the economic ''summit'' conference in the Palace of Versailles, the main allies of the US thought they had a deal with President Reagan over trade with the Soviets. Mr. Reagan would withdraw his objections to the Soviet gas pipeline to Western Europe and to the joint Japanese-Soviet project for oil exploration off Sakhalin Island. In return the allies would be more cautious about granting trade credits to members of the Soviet bloc.
This week that supposed ''deal'' came unstuck in a big way. To the astonishment of the allies, Mr. Reagan announced a new program of yet tighter economic sanctions against the Soviet Union which seemed to be aimed primarily at blocking the pipeline to Western Europe from Siberia and Japanese drilling for oil off Sakhalin.
As though to add insult to injury the Department of Justice in Washington charged 18 electronics officials, including 16 from two of Japan's most prestigious and important corporations - Hitachi and Mitsubishi - of conspiring to steal technical information from an American company, IBM.
The above events expose a condition that is straining and shaking up the American system of alliances. The major friends and allies do not know what American foreign policy is from one day to the next.
There is no clear and consistent body of doctrine that shapes daily decisions. It is as though the Reagan White House closes its foreign policy books at the end of each day and makes decisions the next on a basis of the political expediency of the moment.
The consistent central thread of US foreign policy for the last 30 years has been the cultivation of its system of alliances with Western Europe and Japan. But does safe-guarding the alliance come first any more?
If it did, President Reagan would not have launched his new economic sanctions at the expense of the West Europeans - who want access to Siberian natural gas - and at the expense of the Japanese - who want access to the oil believed to be under the continental shelf off Sakhalin. Those projects are important to a number of West European and Japanese companies which have contracts for the pipe-laying, pumping, and oil-drilling equipment. They are important also to the workers who would be employed in those countries.
If the alliance were still the backbone of American foreign policy, would the government in Washington have publicly charged employees of those big Japanese companies with thievery? Could it not have handled the problem (if there is a serious one) quietly, as can usually be done among important friends and allies?
Then there is the uncertainty about Middle East policy. Officially, the US is ''evenhanded'' between Israel and the Arabs. It is seeking the goodwill of both. It purports to want to build a regional consensus in the area embracing both Israel and the Arabs. It sells arms to Egypt, Saudi Arabia, and Jordan on favorable terms.
But when Israel sends its formidable armed forces surging into Lebanon, killing large numbers of Lebanese civilians in the process to the dismay of the whole Arab community and the shocked horror of much of the outside world, President Reagan in effect gives Mr. Begin a green light.
The White House accepted Mr. Begin's program, which calls for the expulsion from Lebanon of all ''foreign'' forces, meaning that Syrians and Palestinians must be expelled, by someone, before Israel ends its invasion and withdraws its troops. In effect, the American President authorized Mr. Begin to continue to use his armed forces in a way that means effective Israeli control over the southern half of Lebanon and over the shape of any new government to be set up in Lebanon.
Reporters in Washington learned that behind both the green light for Israeli action in Lebanon and the new sanctions against the Soviets (at the expense of allies) the President took his decision after wide differences of opinion among his advisers. On Israeli actions in Lebanon the Department of Defense favored putting a curb on the Israelis, but Secretary of State Alexander M. Haig Jr. favored letting the Israelis go ahead with their campaign.
The roles were reversed on Soviet sanctions. In that argument Secretary Haig favored a pro-alliance policy, whereas Secretary of Defense Caspar W. Weinberger wanted the sanctions.
How can any foreign government understand a foreign policy that agrees at Versailles in early June to drop the sanctions against the pipeline and oil drilling by the most essential allies and then, in late June, flips over and outrages the same allies?
And how does one explain the tolerance for the killing in Lebanon when there is such continued outrage at the denial of civil liberties in Poland?
Mr. Reagan's neoconservative supporters want maximum sanctions against the Soviets and maximum tolerance for what Israel thinks is in its interest. Mr. Reagan at Versailles listened to his professional foreign policy advisers. But back in Washington he must have come under renewed pressure from his most conservative backers.
The only plausible explanation of such inconsistency in foreign policy is that there simply is no established body of foreign policy doctrine in the thinking of the present administration.
It is not pursuing foreign policy. It reacts to domestic political pressures. This strains the alliance and causes confusion.
The Reagan administration has been remarkably consistent in domestic economic policies. The President has a clear and consistent sense about purposes and priorities. There is no doubt about purpose or method, and no surrender.
He seems to be beginning to get results. The American economy appears stronger and steadier than when he took office. Inflation has been brought more under control.
The same cannot be said about Reagan foreign policy. One does not know what to expect next. It seems almost to depend on whether on any given day Secretary Haig or Secretary Weinberger happens to be the more articulate and persuasive.