Washington's harsh words for Japan's stance on the Iranian crisis have brought on a flurry of confusion and defensiveness here that may result in a major U.S.- Japanese controversy.

Shock waves were set off in the government and press by charges from U.S. officials that Japan has been sending "ambiguous signals" to Tehran by purchasing large amounts of high-priced Iranian oil.

A U.S. Senate resolution proposing to censure Japan for these actions was described by one Foreign Ministry official today as "the gravest warning" to Tokyo.

Prime Minister Masayoshi Ohira said he would seek American understanding of Japan's position in light of the pending critical resolution.

In response to the sudden wave of criticism, Japanese officials today said they are caught between the American pressure over the hostages and an Iranian threat to reduce future oil supplies. One well-informed official said he could see no way out unless the hostages are released soon.

Though it has more than 100 days' worth of oil stockpiled, Japan feels it must continue to purchase Iranian oil to ensure future supplies. At the same time, however, Japan has acted recently to curtail the buying of oil on the spot market at unusually high prices, government sources said.

The uproar has also produced confusion in the U.S. Embassy which, sources said, was not informed that the United States would make its attack on Japan for being "insensitive" to the hostage issue when Secretary of State Cyrus Vance met Monday in Paris with Japanese Foreign Minister Saburo Okita.

Sources on both sides said the furor may represent more than simple irritation with the oil purchases. The "blast," said the sources, is more likely the result of what the State Department regards as an overall failure of the Japanese to take a clear-cut position critical of Iran.

"They have sounded too neutral," one american diplomat said today. "It's wishy-washie. they have never really been clear-cut. Some of those hostages are friends of mine. It is really annoying."

Ohira's only major comment on the subject was a brief, carefully worded statement in parliament Nov. 27 that "Japan is watching" the situation in Iran "with deep concern and hopes that the situation will be solved as fast as possible." Through he noted humanitarian considerations, U.S. officials pointed out Ohira's failure to mention legal and moral points against the takeover.