Beirut — For a man whose early days as a diplomat required him to be a stowaway, Yasser Arafat hasn't done too badly. His latest diplomatic victories in Japan and the Soviet Union, and tacit recognition by Greece's new government, have brought his Palestine Liberation Organization one large step closer to its diplomatic zenith - relations with the United States.
These diplomatic forays have coincided with various signals coming from the United States that suggest the US perhaps is considering talking to the PLO:
* Former Presidents Jimmy Carter and Gerald Ford said the United States must talk to the PLO as they were returning from Egyptian President Anwar Sadat's funeral.
* Zbigniew Brzezinski said in an interview with an Arabic magazine, Al Hawadess, recently, that he had met Arafat in 1979 while he was national security adviser for Mr. Carter.
* Former President Richard Nixon visited Saudi Arabia and Jordan on what he called a private visit but what Arab observers called a sounding-out mission for the Reagan administration.
The Palestinians agree that these incidents were not accidental, but they see them as contrived to form a smokescreen.
''All this shows the hint to the future direction of US policy, but when will a real change come? There is nothing substantive now,'' said Mahmoud Labadi, PLO foreign press spokesman.
Shafik al-Hout, a member of the PLO Central Committee, just returned from the United States where he detected panic in US policy because of Mr. Sadat's death, but no sign of warming up to the PLO.
Another well-placed Palestinian source explains the US manuevering in blunter terms.
''They are throwing out these little bits just to keep everyone cool while they figure out what to do now that Sadat is dead. We've seen this happen many times when the United States has no policy ready and needs to buy time,'' said a Palestinian source close to Arafat's office.
Lacking anything tangible from the US, the Palestinians are more excited about the gains they have made in Japan and the Soviet Union.
''Going to Japan was like going to the United States,'' the Palestinian source said.
''Japan was very important because it is a superpower - an economic superpower and part of the Western Alliance,'' Labadi said. ''Both Japan and the Soviet Union were major diplomatic successes for the PLO. . . . They enhance the prestige of the PLO and of the chairman personally,'' he added.
Labadi and al-Hout admit they did not get as much from Japan as they would have liked - namely recognition as the sole representative of the Palestinians and full diplomatic status for the PLO office in Tokyo.
''We didn't expect diplomatic status but the only reason they haven't given it is because of the United States. . . . They even say it sometimes,'' al-Hout said.
But in the case of the Japanese, the Palestinians are patient because they believe the pressure Japan can exert on its American ally is worth far more than an embassy.
In 1968, Gamal Abdel Nasser, then Egypt's president, smuggled Arafat into the Soviet Union aboard his presidential plane. Now the PLO has won full diplomatic status there - 13 years later.
The Palestinians point out over and over again that contrary to what they call ''naive American notions,'' not all national liberation movements are communist.
''The Soviet Union was not rushing to the PLO,'' al-Hout said, ''at first they treated us like a student group. We have not in most cases chosen our friends, they have chosen us by their political line. If the United States had chosen this line, we would have appreciated this very much,'' he added.
''Arafat has managed to lead a good democracy within the PLO with continuous care that no group should try to color the PLO with any label apart from its genuine one as a national liberation movement,'' al-Hout said.
There are groups within the PLO that are Marxist-Leninist in philosophy, but lately Arafat appears to have been quite successful in making the family tow his line.
''Now 98 percent of our diplomatic efforts are devoted to the West,'' al-Hout noted.
Since the Americans are not visibly ready to talk, the Palestinians are focusing on Western Europe.
Ideally the PLO would like to win over Britain and France so that it would have three traditional American allies giving the United States a friendly, but back-against-the-wall push toward the PLO.
However those next two building blocks to the United States don't look nearly as hopeful as they did just a few months ago.
Noting that Franco-Palestinian relations were way ahead of those with other European countries, al-Hout concedes the PLO ''is not very happy'' with the change in the French government.''
We were just about to get an invitation (from Valery Giscard d'Estaing),'' he said.
The signals from Francois Mitterrand are confusing. The total French policy seems very much more American than Giscard d'Estaing's.
PLO spokesman Labadi cites Margaret Thatcher's pro-Americanness as the key to Britain being next in line for a PLO diplomatic coup.
The Palestinians hope British Foreign Secretary Lord Carrington will meet with Arafat sometime before his term as president of the European Community Council of Ministers expires in January 1982.
Lord Carrington just missed Arafat in Saudi Arabia this week, but Labadi said Arafat would try to meet Carrington either in Beirut or Damascus.
''It is pretty much dead now,'' al-Hout commented, adding that Carrington's presidency has only stalemated Euro-Palestinian relations, rather than advanced them, as the Palestinians had anticipated.
Al-Hout boils the situation down to this:
''We have fighting, a truce, diplomatic efforts, peace initiatives, failure, and then tension again leading to the next fight, and we go around again.''''We have had all that so we are ready for the tension again.''