WASHINGTON — When the commercial tells you, “Beef. It’s What’s for Dinner,” who is doing the talking? Is it the federal government, or is it the Cattlemen’s Beef Board?

The answer to that question might not seem to be of major constitutional significance. But yesterday, it appeared to be the only question on the minds of Supreme Court justices as they weighed yet another First Amendment challenge to a commodity-marketing program in Johanns (formerly Veneman) v. Livestock Marketing Association.

In prior cases involving similar programs that promoted California tree fruit and mushrooms, the federal government defended the programs primarily as valid forms of economic regulation that don’t impinge on the free-speech rights of producers who object to the message. Under that theory, the fruit program was upheld, and the mushroom program was struck down.

Yesterday, the government tried out a new defense, portraying the beef-promotion program as pure “government speech.” The government first made the argument when the mushroom case went to the Supreme Court in 2001, but the Court declined to deal with it because it had not been raised in earlier stages of the case.

The “government speech” argument could be a winning strategy for the government, because it would virtually immunize the programs from First Amendment attack. The Court has said that while the government may not censor private speech, it may decide without much interference what messages it wants to convey to the public.

But during yesterday’s proceeding, it appeared the justices were having trouble with the new argument, mainly because the public would have a hard time knowing that the speech — the promotional advertising for beef — is in fact the government’s.

Cattle ranchers are levied a fee of one dollar a head to pay for the program, and the advertisements have a tagline identifying the Cattlemen’s Beef Board or “America’s Beef Producers” as the sponsors.

But Deputy Solicitor General Edwin Kneedler insisted to the Court that no matter what the labeling is, “These are programs of government speech.” The promotional messages, as well as the research and marketing aspects of the beef program, are controlled completely by the secretary of agriculture, he said. Kneedler urged the Court not to junk the entire program just because of the labeling concerns.

Justice Antonin Scalia asked pointedly, “Does it remain government speech” if it is not labeled as such? “The label isn’t accurate,” said Justice Anthony Kennedy. “The government seems to be hiding the ball,” said Justice David Souter.

Lawyer Gregory Garre, who was defending the program on behalf of the beef industry, insisted that “the government isn’t hiding from this message,” noting that President George W. Bush has urged the public to eat beef. Garre also asserted that the beef promotion is part of an overall government program that conducts research and public education on issues such as mad-cow disease.

The question of whether the government must identify itself as the speaker in order to claim that the beef program amounts to government speech took up an unusually large part of the hourlong argument. When Harvard Law School professor Laurence Tribe rose to argue against the program on behalf of the dissenting cattle ranchers, he made it clear he thought the issue was irrelevant.

The First Amendment violation remains, no matter how the message is identified, Tribe said, because his clients are still being compelled to pay for a message with which they fundamentally disagree. Several times Tribe, a veteran advocate before the Court, conveyed impatience with the justices over how the arguments were proceeding.

At one point, when he described the labeling issue as “an interesting digression,” Scalia sarcastically told Tribe, “Just indulge us. Some of us think it might make a difference.”

Tribe was able to tell the justices why some of his client cattle ranchers object to the seemingly beneficial pro-beef messages. While beef sales have increased in recent years, Tribe said, small producers have not benefited. “When the price of beef goes up, the profit is pocketed by meatpackers and restaurants,” Tribe said. He also said that some ranchers who produce dairy cows, for example, view their product as cattle, not beef, and they object to paying for the promotion of beef.

Tribe did acknowledge that if the assessment levied on cattle producers were in the form of an excise tax that went into the general treasury — rather than a fee that went directly to the beef-promotion program — his First Amendment concerns would diminish.

Justices also seemed worried about the impact of their ruling on other marketing programs, as well as on efforts to force the tobacco industry to pay for anti-smoking messages.

Tribe said that cigarette makers could be required to carry the surgeon general’s anti-tobacco message on their packaging, but he did not appear to satisfy the justices on whether the industry could constitutionally be forced to pay for anti-smoking advertising if the Court rules in favor of the dissenting beef producers.

By the end of the hour, it appeared that even though the beef case represented the Court’s third full-fledged consideration of free speech and government-marketing programs, it was still an unsettled area of the Court’s First Amendment jurisprudence.