WASHINGTON  If the Supreme Court does not act, the solicitor general of the United States somberly told its justices on Tuesday, the children of America may be in for some rude surprises.

“The world that the networks are asking you to adopt here today, where the networks are free to use expletives,” said Gregory G. Garre, the solicitor general, may include “the extreme example of Big Bird dropping the F-bomb on ‘Sesame Street.’ ”

In a lively argument heavy on euphemism and concern for the state of the culture, the Supreme Court considered the role of the Federal Communications Commission in regulating “fleeting expletives” on broadcast television  essentially, whether the government can penalize a network for letting a dirty word slip onto the air.

The narrow question before the court was whether the commission had given a sound reason for changing its approach to the treatment of isolated, as opposed to repeated, swearing.