K By Alan Sipress and Ellen Nakashima

UTA, Indonesia, Oct. 16 – Indonesian investigators have recovered traces of C-4 plastic explosives at the scene of the bombing Saturday night in Bali that killed at least 181 people, National Police Chief Da’i Bachtiar said.

The material is similar to the explosives used to bomb the residence of the Philippine ambassador in Jakarta in August 2000, an attack that Philippine intelligence officials have blamed on a radical Islamic network known as Jemaah Islamiah.

That group, which Western and regional intelligence officials say is headed by radical Indonesian cleric Abubakar Baasyir, is active in several Southeast Asian countries. Baasyir has denied involvement in the Bali bombing.

The police chief, Bachtiar, also said Tuesday that investigators were “intensively” interrogating two other men in connection with the attack. Police officials said one was a guard who witnessed the attack and the other was related to a person whose identification card was recovered at the scene. Police said they have questioned about 50 people.

Early Wednesday, an Indonesian security official said authorities had detained a former military officer who might have assembled the bomb.

Another government official, however, cautioned that it remains unclear whether the man, whose arrest is expected to be announced shortly, is responsible. This official said the Indonesian joint terrorism task force is moving closer to the suspected perpetrators.

“We are very close and have enough information to follow the right direction,” the official said.

Meanwhile, the United States and other countries continued to pressure the government of President Megawati Sukarnoputri to crack down hard on its homegrown militants.

“This has been a very sobering experience for the Indonesian leadership when they see this kind of tragedy,” Secretary of State Colin Powell said in Washington on Tuesday. “So we now can see that you are not exempt from this; you cannot pretend it doesn’t exist in your country. It exists everywhere where conditions are right and where this kind of terrorist organization can thrive. And that’s why we have to go after them wherever they are.”

In the week leading up to the Bali bombing, senior U.S. officials repeatedly warned Megawati’s government that they believed militants in Indonesia from Osama bin Laden’s al-Qaida network were planning attacks on American targets, according to U.S. and Indonesian officials.

U.S. Ambassador Ralph Boyce raised these concerns on several occasions with Megawati and her top security advisers. He also arranged last week to have Adm. Thomas Fargo, commander in chief of U.S. Pacific Command, call the influential chief of the Indonesian military, Endriartono Sutarto, to press U.S. concerns that extremists linked with Jemaah Islamiah were posing an urgent threat to Americans, according to senior officials from both countries.

Senior U.S. officials made clear that the Bush administration would withdraw many diplomats and embassy families from Jakarta unless Indonesian authorities stepped up their efforts to investigate and capture suspected militants. After the attack in Bali, U.S. officials moved immediately to pull nonessential diplomats and embassy families from Indonesia.

Megawati and her Cabinet greeted the warnings with skepticism, particularly those concerning Jemaah Islamiah. To persuade the Indonesians that intelligence about the Jamaah Islamiah was genuine, the Americans permitted Indonesian authorities to question Omar al-Farouq, a Kuwaiti operative linked to al-Qaida.

The U.S. officials said they expected action from Indonesia’s security forces before Megawati is expected to meet President Bush on the margins of the Asia-Pacific Economic Cooperation forum meeting next week in Mexico, according to sources familiar with the conversations.

Indonesian government officials said that Megawati plans to announce an emergency law this week that would give authorities new powers to apprehend suspected terrorists. The law, which would be in force for one year and then would be subject to parliamentary approval, would enable anti-terrorism investigators to hold suspects for at least seven days without charging them.

One of Indonesia’s most violent Islamic militant groups, Laskar Jihad, announced Tuesday that it was disbanding and suspending operations in the eastern region of the Moluccas islands, where radical militiamen two years ago intervened on the side of local Muslims feuding with the neighboring Christian community. Thousands have been killed in clashes in the Moluccas.