President Reagan's measure as a leader of the Western world will be taken next week when he crosses the Atlantic for 10 days of grand-tour diplomacy.
The trek, Mr. Reagan's first away from the New World since he took office, will be grueling - with no less than two crucial summits, on the basic global themes of butter and guns: first the yearly gathering of the seven major Western industrial powers at Versailles June 4 to 6, later the meeting of 15 NATO alliance chiefs in Bonn June 9 and 10.
Strung between the summits will be state and papal visits in Rome, a sojourn at Windsor Castle in Britain. The tour's planned finale: a Reagan address at the Berlin Wall, symbol of the cold war's costs, where the American President's tone and conclusions could set the pace for the imminent superpower strategic arms talks and Reagan-Brezhnev summit.
Some American and European officials say frankly they had hoped more for specific deals in the groundlaying for the summits. Crowding so many events into less than a fortnight in Europe - a tour structured more like an American political campaign, keyed to nightly news visuals - works against forging pacts on the spot.
But a broad consensus was reached among the participants to avoid open rows and to stress instead several themes:
* US commitment to Europe. Mr. Reagan's trip abroad, coming after visits to border nations Mexico and Canada, is intended to reaffirm the United States' ties to Europe, as against the go-it-alone tendencies of some of the President's domestic backers. This is taken by Europeans as a reassuring and timely gesture of moderate influence, if not the final word on Reagan global priorities. How Reagan comes across to the European public will be closely watched.
* The West's economic tensions. The ''sherpas,'' or the advance economic aides shaping the terms of the Versailles summit, settled on four basic issues:
First, the impact of US interest rates on the other economies would be discussed by the leaders, perhaps in a context by then of a budget decision in Congress - but Reagan would promise no concessions in his domestic macro-economic policies.
Second, on trade, the Japanese would be leaned on to devalue the yen or otherwise open their domestic market to competitors, protectionist sentiments rising again in the West would be denounced, and plans for a new round of trade talks in November would be affirmed.
Third, a deal would be sought to tighten credit conditions for the West's sales to the Soviets.
Finally, a proposal by the host French to consider the impact of technology on Western job markets would get a polite hearing, then deferral for study. Other subjects like North-South relations, or the needs of developing nations, would get cursory treatment. And much of the private talk would turn to topics like the Falklands, and Middle East initiatives.
* East-West strategic policy. The Europeans acknowledge Reagan's zero option plan for removing intermediate weapons from Europe, and his May 9 Eureka College proposal to reduce US and Soviet long-range nuclear arsenals, were the kinds of steps needed before Reagan could touch European soil without provoking public outbursts. As it is, demonstrations are expected. The last critical card in Reagan's nuclear negotiating hand could announced Memorial Day weekend - a willingness to abide by SALT I and SALT II documents as an interim step while START talks begin.
The NATO session in Bonn is intended to show alliance ''unity, firmness, and cohesion,'' according to Western officials. It should reflect a ''reconfirmed convergence'' of US and European views. The basis for a new posture between NATO and the Soviet bloc could emerge, with three touchstones: resumption of arms reduction talks, continued pressure on the East to lift repressive policies in Poland, and an agreement on Western subsidized credits to accommodate in limited fashion Reagan's preference for economic containment of the Soviet Bloc.
* Separate political agendas. Several Western leaders, in addition to Reagan, stand to benefit from the summit exposure. West German Chancellor Helmut Schmidt has been in a fix over deployment of US intermediate range missiles in Europe. The missiles were originally intended to offset a Soviet strike, but their purpose became confused with talk of waging an East-West war, with Europe as a battleground. The Italians appreciate inclusion among the four European powers selected for a Reagan visit, and are waiting until after Reagan departs and UN arms talks in New York for their next verifica in late June - the Italian term for deciding whether to dissolve the government and form a new ruling coalition, next possibly led by the Socialists.
For the British, caught in a Common Market dispute in addition to the Falklands crisis, the Reagan visit's timing June 7-9, could be either good or bad, depending on the flow of South Atlantic events. Prime Minister Margaret Thatcher gets on well with the President, and the two-day visit to Britain is seen as a personal highlight for Reagan.
French President Francois Mitterrand could prove the most difficult leader for Reagan to approach at Versailles. France is the only one of the four European nations visited by Reagan where he will not address the host nation in a live televised address. Yet Mr. Mitterrand has taken preparations for the summit seriously, intent on showing that his Socialist government is a responsible Western power.
The Canadians and Japanese stand to be the least pleased by the Versailles summit. Canadian Prime Minister Pierre Trudeau is disappointed at the major powers' indifference to the issue of developing nations, and he is aware that Canada bears perhaps the heaviest impact of US economic policies. The Japanese have lifted an annoying ban on US fruit shipments untreated for the Medfly, and a partial list of trade adjustments was released May 27 to anticipate Versailles trade pressures. But this may not be enough to halt the hostility that appears likely to move Japan's way as protectionist pressures grow in the West from recession and unemployment.
Reagan aides admit that ''public diplomacy'' is one of their chief goals in the Reagan European tour. ''He will be able to reach the European public in a way he hasn't been able to reach them before,'' says White House communications director David Gergen.
Reagan will give live solo televised speeches in Italy, the United Kingdom, Bonn, and Berlin, in addition to exposure in the group gatherings in Versailles.
The potential for negative publicity is also very much on the Reagan staff's mind, either in reports of private bickering among the conferees or in public demonstrations in Berlin, West Germany, or Britain.
The administration thinks its nuclear negotiating position may ease much of the peace protest animus that was building in recent months. And it is counting on a mix of talk and postponement to get past mounting tension in Western governments over recession and interest rates.