WASHINGTON, June 27 — A proposed Constitutional amendment to allow Congress to prohibit desecration of the flag fell a single vote short of approval by the Senate on Tuesday, an excruciatingly close vote that left unresolved a long-running debate over whether the flag is a unique national symbol deserving of special legal standing.

The 66-to-34 vote on the amendment was one vote short of the 67 required to send the amendment to the states for potential ratification as the 28th Amendment. It was the closest proponents of the initiative have come in four Senate votes since the Supreme Court first ruled in 1989 that flag burning was a protected form of free speech.

The opponents — 30 Democrats, 3 Republicans and an independent — asserted that the amendment would amount to tampering with the Bill of Rights in an effort to eliminate relatively rare incidents of burning the flag. They said it violated the very freedoms guaranteed by the symbolism of the flag.

"This objectionable expression is obscene, it is painful, it is unpatriotic," said Senator Daniel Inouye, a Hawaii Democrat who won the Medal of Honor for his service in World War II. "But I believe Americans gave their lives in many wars to make certain all Americans have a right to express themselves, even those who harbor hateful thoughts."