Hundreds of left-wing protesters were preparing to march in Chicago on Monday as the Democratic National Convention got underway nearby, providing an early test of the city’s security preparations and of Vice President Kamala Harris’s attempts to project a sense of intraparty unity.

At least two protest marches were planned for the convention’s opening day, including by a coalition of more than 200 activist groups representing a range of causes that was expected to march within “sight and sound” of the United Center, the main convention hall, on Monday afternoon.

Activists carrying signs with messages like “Free Palestine!” began to gather for that event in Union Park on Monday morning, just west of downtown Chicago, and organizers were expecting thousands or tens of thousands of people to show up. Ellie Feyans-McCool, who traveled from Minnesota to attend the march, said she hoped protesters in Chicago this week would nudge the Democratic Party to withhold future military support for Israel.

“It is no longer good enough just to stand against Trump,” said Ms. Feyans-McCool, who added that she had not yet decided whether she would support Ms. Harris or a third candidate. “You have to do good.”

At one point, a group of about a dozen people with Israeli flags marched around Union Park, leading a small contingent of pro-Palestinian protesters to break off and march alongside them. The Chicago police, which had mostly kept their distance until that point, kept the two groups separated.

Members of the coalition planning the Monday march sued Chicago in federal court over the terms of the protest. Though the activists won some concessions, including permission to have a stage and sound system at a rally before their march, they remained at odds with city leaders over the exact route they would follow.

Hatem Abudayyeh, a spokesman for the coalition and a pro-Palestinian activist, acknowledged on Monday that the turnout was far from the tens of thousands that organizers had hoped for.

“It’s a Monday morning, which in and of itself is not the greatest starting time, but we needed to do it because we wanted to have protesting happening as soon as the thing started,” he said.

But he was hopeful that more would converge on Chicago over the week and maintain a steady showing through Thursday, the last day of the convention.

City officials, exhausted and frustrated by comparisons to the chaotic 1968 Democratic National Convention in Chicago, have sought to convey a sense of calm and confidence in recent weeks.

Mayor Brandon Johnson, a first-term Democrat, has emphasized his own experience leading demonstrations with the Chicago Teachers Union. He has insisted that the city is ready to a host a safe convention where protesters can gather peacefully but violence will not be tolerated.

The Chicago police superintendent, Larry Snelling, said that a protest on Sunday night showed that the city was prepared. During that event, hundreds of demonstrators marched down Michigan Avenue as they called for the protection of abortion and L.G.B.T.Q. rights, and peace in Gaza.

“Our officers responded exactly the way we trained them to respect First Amendment activity,” Mr. Snelling said.

One 23-year-old woman was arrested nearby on Sunday and charged with defacement of property and obstructing a police officer, he said. The woman was not part of a march, he said.

Some who attended Sunday’s protest said they were taken aback by the large number of officers who lined Michigan Avenue on bicycles and followed the march.

“You almost see more police than marchers here — it’s overkill,” said Rabbi Brant Rosen, who leads a congregation in Chicago and was among the marchers.

Unlike at the Republican National Convention in Milwaukee last month, where protests were mostly contained to the first day, activists from different groups have announced plans to gather on every day of the Democratic convention in Chicago.

Alex Nelson, who lives in Chicago, planned to be at several of them and had taken time off from work to participate.

“My hope is that things continue to be peaceful,” she said, “and that the mayor, the governor and the police continue to allow us to demonstrate and march and exercise our First Amendment rights.”

Julie Bosman contributed reporting.