BEIRUT, Lebanon — When the Lebanese authorities announced the arrest of an Israeli spy ring late last year, the news aroused little surprise. It is no secret that Israel has long maintained intelligence agents here.

But in recent weeks, more and more suspects have been captured, including a retired general, several security officials and a deputy mayor. All told, at least 21 people have been arrested, and 3 others escaped over the border into Israel with the help of the Israeli military, Lebanese officials say.

The spying network’s extent has mesmerized the Lebanese and made headlines here. It has also infuriated Lebanese officials, who sent an official protest to the United Nations this week. On Friday, President Michel Suleiman complained about the matter in a meeting here with Vice President Joseph R. Biden Jr.

The arrests appear to reflect a newly energized and coordinated effort by the Lebanese security agencies, which now cooperate far more effectively among themselves and with Hezbollah, the Shiite militant group based here, than they did in the past.

“New technologies have helped in catching them,” said Gen. Ashraf Rifi, the director of the Internal Security Forces. “But we have also had better cooperation with the army than we had before.”

Those accused of being spies are said to have used sophisticated surveillance equipment and satellite phones, sometimes ingeniously disguised in crutches or knapsacks. One of them, a car dealer in southern Lebanon, placed Israeli tracking devices in cars he sold to Hezbollah members, security officials say. Most seem to have been motivated by the promise of money. Some were caught by Hezbollah before being handed over to the Lebanese authorities.

The arrests have even become an issue in Lebanon’s coming parliamentary elections, with some analysts saying that, intentionally or not, they might benefit the political alliance led by Hezbollah, Israel’s primary nemesis here. Hassan Nasrallah, the leader of Hezbollah, delivered an angry speech on Friday in which he called for all the captured spies to be executed and urged the Lebanese to help in capturing any remaining agents.

“Everyone who proves to be lenient in this business will be considered a partner” of Israel, Mr. Nasrallah said, noting that some of the spies had been captured with explosives and weapons, not just surveillance devices.

Hundreds of Lebanese spied for Israel during its 18-year occupation of southern Lebanon, most on a short-term basis. Many were southerners who felt they had no choice, and they were forgiven, or they served short prison terms after the Israeli withdrawal in 2000. But since then feelings have hardened toward those who spy for Israel, which waged a punishing bombing campaign here during its war with Hezbollah in 2006. Those convicted of spying can face the death penalty under Lebanese law.

Of the 21 accused of being spies who have been arrested in the past year, 13 played an important role, General Rifi said, and the others were relatively insignificant.

One of the important ones, the general said, was Ziyad Homsi.

Mr. Homsi, 61, was the deputy mayor of Saadnayel, a town in the Bekaa Valley. According to a report in the Lebanese newspaper Al Safir, which has links to Hezbollah, Mr. Homsi had told interrogators he was assigned to meet Mr. Nasrallah, which he apparently failed to do. Israeli monitors planned to track his movements as he went to meet the Hezbollah leader.

Mr. Homsi, who was arrested on May 16, said that he had started working for Israel because he needed the money, the newspaper reported, and that he had been paid $100,000.

Many friends and relatives of those accused of being spies say they cannot believe the accusations. “He’s been a friend for more than 18 years,” Issam Rouhaymi, the mayor of Saadnayel, said about Mr. Homsi. “Nobody could believe such a thing.”

Mr. Homsi was active in the Future Movement, the pro-American political party that is opposed to Hezbollah. Mr. Homsi’s brother said the charges had been manufactured to damage the party’s chances in the elections.

Investigators said that Mr. Homsi, like many others accused of being spies, traveled abroad to meet with Israeli agents, who provided him with instructions and equipment.

Some contrived elaborate schemes to avoid detection. Ali al-Jarrah, who was arrested last year and accused of spying for Israel for 25 years, had two homes and two wives who did not know of each other. Adib al-Alam, a retired general arrested in April, had established a domestic maid service at the behest of his Israeli spymasters, officials have said. He used it to disguise his telephone calls and trips abroad to meet with Israeli officers.

Perhaps most infuriating of all, for Lebanese investigators, was what happened this week. On Sunday and Monday, two people accused of being spies escaped across the southern border into Israel, one of them bringing his family with him, according to a Lebanese government complaint submitted to the United Nations. The Israeli military helped them escape, the report states. Another man staged a similar escape this month.

It must have been a daring and risky escape, passing through Hezbollah’s home terrain and across a fenced and guarded border. But it is not impossible.

“There are crossing points,” said Timur Goksel, a former senior adviser of the United Nations peacekeeping force in Lebanon. “But I don’t think the Israelis would help just anyone cross over. It would have to be someone they saw as important.”