BERKELEY, Mo. — Demonstrators hoping to block Interstate 70 here on Wednesday to protest the fatal shooting of Michael Brown a month ago were barred by the police from entering the highway. The authorities said 35 people had been arrested, most for unlawful assembly but four for assaulting officers.

As traffic continued to move during the late-afternoon rush, demonstrators and police officers, some in riot gear, faced each other in a standoff, at times tense, on North Hanley Road at Interstate 70 near the St. Louis airport. The several dozen demonstrators were outnumbered by more than 100 officers from three law enforcement agencies.

One demonstrator, Charles Brooks, was among those who sat down in the road, shouting: “McCulloch got to go! McCulloch got to go!” — a reference to the St. Louis County prosecutor, Robert P. McCulloch, whose office is investigating the shooting. Asked why he had joined the protest, Mr. Brooks said, “I want to see justice served here.” Seconds later, he was picked up by officers, handcuffed and led to a bus from the Missouri Department of Corrections.

Although the demonstration, which formed shortly after 3 p.m., was generally peaceful, a handful of protesters hurled objects at officers, including, the authorities said, bricks, stones, glass bottles and water bottles. But protesters said the presence of riot-ready police officers was unnecessary and agitated many in the crowd.