“PREPOSTEROUS,” SAID a U.S. Embassy spokesman in Tokyo. That is a charitable characterization of ahistorical and offensive statements by leaders of Japan’s public broadcasting network, NHK.

First it was Katsuto Momii, the newly installed head of the network, who said that all countries involved in World War II provided “comfort women” to their soldiers. In fact, “comfort women” is a euphemism for a uniquely Japanese system that enslaved thousands of women, mostly Korean, transported them to military bases and forced them to engage in sex — to be routinely raped by Japanese servicemen. In many cases the enslavement lasted for years, and many of the women died.

Then NHK board member Naoki Hyakuta denied that the 1937 Nanjing massacre occurred and said the United States staged its trials of alleged Japanese war criminals after Japan’s defeat in 1945 to cover up U.S. war crimes. It was the latter slander that caused the U.S. Embassy to tell Time magazine that “these suggestions are preposterous.”

Why can’t Japan’s government bring itself to condemn these comments with equal clarity? When neighboring countries complain about Japanese attempts to rewrite or sugarcoat the history of World War II, Japanese officials like to point out that they can’t infringe on freedom of speech. Unlike in China, where honest discussion of historical subjects can get someone thrown in prison, Japanese are free to say what they like.

But Prime Minister Shinzo Abe is also free to speak up, and his responsibility is particularly heavy in this case because he appointed Mr. Hyakuta to the board and engineered Mr. Momii’s installation in December. It’s not enough, as Japanese officials often do, to point to the remorse that some previous leader expressed years ago. Nor is it enough to deflect the offensive remarks by saying, as a government spokesman did, “Our understanding is that Chairman Momii made the comment as an individual.”

In fact, statements Mr. Momii made in his official capacity are just as alarming, because he also suggested that the network — long admired for its independence and professionalism — should tilt toward a government line. “It would not do for us to say ‘left’ when the government is saying ‘right,’ ” he said. The prime minister, to his credit, then urged “all NHK employees, beginning with director Momii, to continue broadcasting fairly and impartially.” But the shadow of government pressure and the danger of self-censorship will not be easily erased.

Most of Mr. Abe’s agenda makes sense for Japan and the U.S.-Japan alliance. He is trying to get Japan’s economy growing again, negotiate a free-trade agreement with the United States and other Pacific nations and slightly increase Japan’s defense budget and reinterpret its laws so that it can play a more useful role as an ally.

But these policies are undermined by the kind of obtuseness reflected in the NHK flap. The rewriting of history helps those who would paint as dangerous militarism Japan’s legitimate efforts to bolster its international role. U.S. officials, too, are wondering whether Mr. Abe is primarily a nationalist or primarily a reformer. Only he can make clear whether he supports an independent press and rejects destructive historical denialism.