Several thousand Palestinians, many of them schoolchildren bused in from their classes, joined peaceful protests in the Gaza Strip along sections of the border with Israel for several hours on Monday, forming human chains in some locations as part of a public campaign against the Israeli blockade.

But the turnout, estimated at about 5,000, was far smaller than had been expected, and fears in Israel that masses of Gaza residents might try to break through the Israeli-built barrier along the border, as they breached the border with Egypt last month, proved unfounded. Most protesters kept a safe distance from the barrier.

The demonstrators dispersed around noon, and shortly after militants in Gaza fired a number of rockets at Israel. One landed outside an apartment block in the Israeli border town of Sderot. A boy, Yossi Yadlin Haimov, 10, was badly wounded in the shoulder by shrapnel and underwent surgery at a hospital in Ashkelon.

In northern Gaza, some of the protesters started marching toward the Erez crossing, but they were stopped by a line of armed Hamas policemen. The police officers blocked the road about half a mile south of the crossing, seeking to prevent a confrontation with Israel.

After the main protest ended, a group of Palestinian youths rioted at the crossing, throwing stones. When they tried to cross, Israeli troops fired shots into the air, an army spokeswoman said, speaking on condition of anonymity under army rules. She said an Israeli officer was slightly wounded in the clash. At least two Palestinians were wounded, according to Palestinian reports. The spokeswoman said 49 Palestinians had been arrested.

Palestinian advocates had called for Gaza residents to form a human chain along the roughly 30-mile border with Israel from Rafah in the south to Beit Hanoun in the north to protest Israel’s closure of the main passages into Gaza since the Islamic militant group Hamas took control there last June. Israel recently tightened the blockade in response to intensified rocket fire from the strip.

Despite the low numbers, the main organizer of the protest, Jamal el-Khoudary, declared the event a success. “It was peaceful, and that was what we were aiming for,” said Mr. Khoudary, an independent lawmaker in Gaza with ties to Hamas.

Hamas leaders have been encouraged by recent calls by European officials for Israel to reopen the passages to Gaza and ease the conditions of the 1.5 million residents of the strip.

On Monday, though, fear kept many Gazans at home: the Israeli Army made it clear that it was taking the threat of a border breach very seriously, and thousands of extra troops and police officers were deployed along the Israeli side of the barrier.

A joint statement released by the offices of the Israeli foreign minister and defense minister on Sunday night said, “Israel does not interfere in demonstrations taking place inside the Gaza Strip, but Israel will protect its borders and will prevent any violations of its sovereign territory.” If the situation did deteriorate into violence, the statement warned, Israel would lay sole responsibility for the consequences on the shoulders of Hamas, which had placed Palestinian civilians “on the front lines.”

Israel bolstered its artillery units along the border and occasionally fired smoke bombs, either to conceal troop movements or deter the protesters. Soldiers in full camouflage hid in the lush green wheat fields of Israeli farming communities near the border line. As the tension dissipated, the soldiers picnicked on army rations to the sound of a loud chorus of muezzins calling the faithful to midday prayers in mosques on the other side of the barrier.

The deputy defense minister of Israel, Matan Vilnai, told Army Radio on Monday evening that the deployment of the security forces, led by the army, was the main factor that led the Palestinians “to rethink whatever they were doing.”

But there was also a feeling on both sides that the event on Monday was an exercise or rehearsal for another time.

A Hamas lawmaker, Ismail al-Ashqar, said at the protest in northern Gaza on Monday, “If the world does not respond and end the siege, then what is coming will be worse.”

Another Hamas lawmaker, Yihya Musa, threatened that the human chain formed Monday could in the future turn into a series of “bombs ready to explode.”

Separately, an American tourist drowned Monday in a flash flood while hiking in a riverbed near the Dead Sea, an Israeli police spokesman said. The spokesman, Micky Rosenfeld, identified the tourist as David Tauber, in his mid-30s, from New York. Rescue units searched for a woman who had been hiking with Mr. Tauber and found her alive, Mr. Rosenfeld said.