London — West European governments are again being forced to rethink their view of President Reagan as an ally and as head of the world's most powerful country. The President's decision to send marines into the Caribbean island of Grenada is only one reason for renewed doubts about his competence and coolness as a world leader.
There is a rising belief in Western European capitals that Mr. Reagan has allowed himself to drift into a Middle East quagmire, with the United States commitment to the multinational peacekeeping force in Lebanon now openly questioned as a basis for future policy in the region.
In Paris, foreign ministers of the four countries contributing to the force were set for an urgent meeting to consider the future of the multinational force. US Secretary of State George Shultz was preparing for blunt indications from his British and French counterparts that the Europeans see no long-term future for the force.
Mr. Reagan's decision to brush aside Prime Minister Margaret Thatcher's objections to the Grenada invasion is seen by Britons as undermining the special relationship between London and Washington. Leading opposition and some government politicians are saying the President cannot be trusted any longer.
A startling aspect of these negative opinions is the speed with which they have developed.
In Western Europe Mr. Reagan's reputation as a world leader had been enhanced in recent months by the flexibility he had shown at the nuclear arms talks at Geneva.
Following the shooting down of the South Korean airliner by the Soviets, he gained more points by acting in a statesmanlike way and outclassing the Soviet leadership in his ''feel'' for the crisis.
Now suddenly renewed doubts are arising about sensitivity in dealing with potentially touchy allies and asserting US power in world trouble spots.
In Britain, Labour opposition shadow foreign secretary Denis Healey declared that Reagan erred badly in ordering the invasion of Grenada, a member of the British Commonwealth, against Mrs. Thatcher's clearly spelled-out advice.
Especially disturbing was Mr. Healey's linking of the Grenada question to the impending deployment of US medium-range nuclear missiles in Britain and other West European countries.
''President Reagan has shown by his Caribbean action that his administration cannot command confidence, for example, in arrangements for controlling and if necessary firing cruise missiles,'' he said.
Privately, British government leaders are furious about what they see as Reagan's rough handling of the Grenada crisis. Foreign Secretary Sir Geoffrey Howe was criticized by members of his own party for failing to condemn outright the US action.
Similar sentiments have been expressed in France. An official statement issued in Paris condemned the Grenada invasion as illegal and unwise.
President Francois Mitterrand in recent months has strongly supported Reagan's handling of the Geneva arms talks. He applauded the Reagan line on the Korean airliner incident.
Now French diplomats speak coldly of a US administration acting without sufficient consideration for friends and allies. Earlier this year France and the US clashed over how to deal with Libyan pressures in Chad. Similar tensions were evoked by developments in Grenada.
Staff writer Elizabeth Pond in Bonn reports: The invasion of Grenada is ''dreadful'' in its negative impact on European public opionion, a retired West German general says.
His view is representative of the private - if not public - feelings of Bonn's center-right government. Officially, criticism of the US is much more muted here than from Britain, Canada, and other US allies. But privately, officials worry about the effect of the Grenada adventure a month before controversial new NATO missile deployments are to begin.
Before Grenada, explained the ex-general, ''We could argue (to peace protesters) that America was only defensive,'' while the Soviet Union was expansionist. Now, US action in Grenada has ''devalued'' the argument about Soviet aggression in Afghanistan by making the US look indistinguishable from the Soviet Union.
The retired general was attending a security conference of the newly formed Strategic Forum.
Other active and retired West German military officers and ambassadors echoed this view. They fear Grenada could upset the grudging domestic consensus they think they had finally won for NATO deployment of the new American missiles. And they question Washington's priorities in placing this delicate consensus at risk by what they view as a minor victory in the Caribbean that makes the US look like a bully.
The American invasion is seen as reinforcing the peace movement's image of America as trigger-happy, even in areas of little strategic importance. Bonn's worry is that the Grenada attack could stimulate anti-American sentiment here and undo the impact of the Soviet shooting down of the Korean airliner last month. Public revulsion over that incident overshadowed this fall's initial antinuclear demonstrations.
But in public, no Bonn government official wishes to criticize the White House. Foreign Minister Hans-Dietrich Genscher has confined his comments to regret over the loss of life in Grenada.
Similarly, a parliamentary spokesman for the Christian Democratic Party has voiced the expectation that the US action was undertaken to protect US lives and that the mission will soon be completed.