China formally charged a prominent Hong Kong journalist with spying for Taiwan on Friday, ratcheting up a politically sensitive investigation that has also resulted in the arrest of a mainland scholar with ties to China's president, Hu Jintao.

The government decided to charge Ching Cheong, chief China correspondent for the Straits Times newspaper of Singapore, despite appeals for his release from Hong Kong political figures and international media organizations. But Ching's family held out hope that the authorities might expel him after a quick trial rather than sentence him to prison.

Ching, 55, considered one of the most knowledgeable reporters covering China, is the first journalist from Hong Kong to be accused of espionage by the Beijing government since the former British colony's return to Chinese sovereignty in 1997. If convicted, he could also be the first correspondent for a foreign newspaper to be imprisoned in China since Mao Zedong's Cultural Revolution.

State security agents detained Ching on April 22 in the southern city of Guangzhou, where his wife and editors said he was trying to obtain a manuscript by an author who secretly conducted years of interviews with Zhao Ziyang, the Communist leader purged for opposing the 1989 Tiananmen Square massacre.

Ching's wife later accused the government of luring him to the mainland and detaining him in an attempt to get information about the manuscript and to intimidate other journalists and publishers from trying to obtain it. China's Foreign Ministry immediately denied the allegation, saying Ching was detained on suspicion of espionage.

About the same time, the authorities detained two scholars at a government research organization, the Chinese Academy of Social Sciences: Lu Jianhua, a well-known sociologist who is a longtime friend of Ching, and Chen Hui, an influential official in the academy's administration.

Lu, 45, was considered a rising star in political and academic circles and appeared regularly on state television as a commentator. In recent years, he was working to develop a relationship with the office of President Hu and sometimes presented himself as an informal adviser with ties to the president.

A colleague of Lu and Chen, who spoke on condition of anonymity, said the men also enjoyed good relations with officials in the government's intelligence apparatus. He said it was extremely unusual for the authorities to detain such well-connected individuals, suggesting that the investigation was a politically motivated attempt by Hu's rivals to embarrass the president.

The colleague said Lu made enemies by advocating more moderate policies toward Hong Kong and Taiwan. Lu also provided Hu's office with independent assessments of the politics of both territories that sometimes contradicted reports provided by the government's traditional policymaking bureaucracy, the colleague said.

The exact nature of the charges against the two scholars remained uncertain, but the colleague said that Chen was suspected of providing Lu with such classified material as copies of Hu's internal speeches, and that Lu was suspected of sharing the material with Ching.

Reached by phone, Lu's wife, Qu Liqiu, confirmed that her husband had been detained and said she was very concerned. She declined to comment further. Chen's family could not be reached for comment.

Ching's wife, Mary Lau, said Lu visited her husband in Hong Kong last year. He sought Ching's help in arranging meetings with a wide range of political figures, including members of the pro-democracy movement, and said he was preparing a report on Hong Kong's political situation for the leadership, she said.

Lau said Lu also sought Ching's views on the mainland's policies toward Taiwan. She said Lu seemed excited when she and her husband submitted a paper urging that the Beijing government reach out to the island's opposition parties and invite their leaders to the mainland for talks.

State security agents detained Ching just days before the historic April visit to the mainland by Lien Chan, then chairman of Taiwan's Nationalist Party. The date of Lu's arrest is unknown, but colleagues said he stopped showing up at work in April, and Chen disappeared from view in May.

One mainland analyst said the arrests might have disrupted Hu's talks with Lien and with another Taiwanese opposition leader, James Soong, the following month, leading him to take a more cautious position and offer fewer concessions. Hong Kong media have suggested that Ching passed information about Hu's negotiating position to the Taiwanese.

Lau has repeatedly denied that her husband is a spy. But reached by phone on Friday, she declined to repeat the denial, saying she was worried that doing so might hurt her husband's case in court. She said she believed the government might yet release him.

"I hope this case is coming to a close, but it's difficult to anticipate what will happen next," she said. "I don't think it's going to be easy."

Detailing the charges against Ching for the first time, the official New China News Agency said Friday that he was recruited by Taiwan's National Security Bureau in early 2000 and "obtained through buying or other means a great deal of information about China's political, economic and especially military affairs, including some classified as 'top secret' or 'confidential.' "

In Taipei, Michael You, an official with Taiwan's Mainland Affairs Council, which handles relations with Beijing, said he had no information about whether Ching was spying for his government, according to Reuters.

Neither Ching's lawyers nor his relatives have been permitted to see him since his detention.

Ching Cheong was said to be trying to get a manuscript of talks with a critic of the Tiananmen massacre.