HARARE, Zimbabwe — More than a quarter of President Robert Mugabe’s opponents in Parliament have been arrested since agreeing to join the government in a shaky power-sharing arrangement, part of an intensifying campaign of harassment intended to drive them out of office, officials from both sides say.

Ever since the two wings of the Movement for Democratic Change, the party founded to fight Mr. Mugabe’s rule, accepted a power-sharing arrangement with the government in 2008, about 30 of their 109 members of Parliament have been arrested at one point or another, with some of them being taken into court shackled in leg irons, according to human rights lawyers and the M.D.C.

“They’re trying to force us out, and they’re not sophisticated enough to hide it,” Elton Mangoma, a cabinet member and M.D.C. leader who helped negotiate the troubled power-sharing deal, said between two recent stints in jail.

The latest arrest of an opponent came on Friday, despite warnings from Zimbabwe’s neighbors that such detentions must stop. The police accused Moses Mzila Ndlovu, co-minister for national healing, of attending a meeting held without their authorization. It was a memorial prayer service for the thousands of civilians from the Ndebele minority slain in the early years of Mr. Mugabe’s 31-year rule.

As Mr. Mugabe, 87, seeks another term, his political anxieties are showing, and not just in the arrests of his opponents. He is also deeply worried about disloyalty in his own party, ZANU-PF, and leaks from insiders about his health and his party’s violent political strategy for the elections it is demanding sometime this year.

At a funeral last Thursday for a leader of his vast spy service, Mr. Mugabe complained about party members who “run to our enemies to tell them the details of our meetings.” And he warned these “sellouts” that intelligence agents were watching them.

There are now two aggressive new newspapers in Zimbabwe challenging the state’s version of reality, and as an ill-concealed battle rages in Mr. Mugabe’s own party to succeed him, some ZANU-PF officials are maneuvering to advance their own interests.

“Now that he’s clearly old, the different factions are moving in,” said Dewa Mavhinga, regional coordinator for the Crisis in Zimbabwe Coalition, an alliance of more than 300 civic groups. “It’s clear there has to be thinking post-Mugabe, most so within his own party.”

The president’s allies are striking out at those who challenge him. Even a sardonic sense of humor can be a criminal offense if the punch lines zing Mr. Mugabe, who controls the police, prosecutors and prisons.

Douglas Mwonzora, an M.D.C. leader who lectures on Roman law at the University of Zimbabwe, recently stood in court, gazing at the omnipresent portrait of Mr. Mugabe. Mr. Mwonzora was handcuffed, shackled and clothed in prison-issue khaki short pants (no underwear allowed), facing a charge, which he denied, of inciting public violence. The magistrate had not arrived yet, so Mr. Mwonzora said he respectfully addressed the portrait.

“How are you, father?” he asked Mr. Mugabe, widely rumored to have prostate cancer. “How is your health?”

People in the courtroom burst out laughing — but on April 8 the police charged Mr. Mwonzora with insulting the president, an offense punishable by up to a year in prison.

Mr. Mwonzora, who heads Parliament’s constitution-making committee for the M.D.C., had already been jailed almost four weeks in February and March before being released on $50 bail. He had slept for days on the concrete floor of a cell, next to a toilet. For weeks, he shared another cell with inmates accused of rape and murder — a cell earlier inhabited by an M.D.C. senator.

“ ‘That’s where we put M.D.C. M.P.’s,’ ” Mr. Mwonzora said prison guards told him.

The menacing buildup to the voting seems like a replay of the violent, rigged elections that have plagued Zimbabwe over the past decade. But calls by ZANU-PF officials for the arrest of the M.D.C.’s leader, Prime Minister Morgan Tsvangirai, seem to have galvanized South Africa’s president, Jacob Zuma — the regional mediator in Zimbabwe’s political crisis — to demand a halt to political arrests and violence.

The efforts to goad Mr. Tsvangirai are many. The police have banned his rallies and arrested his drivers for using blue beacon lights without authorization. The state-controlled Sunday Mail newspaper published rumors that Mr. Tsvangirai, a widower, was sleeping around, accompanied by a photograph of him being hugged by someone the paper described as “that unidentified white woman.”

But Mr. Tsvangirai, who has survived arrests, a police beating, assassination attempts and a treason trial over the past decade, insists that he will not quit the government, no matter the provocation.

“They want to push you out so they can run the elections under their own conditions,” he said.

Already, ZANU-PF is cranking up the electoral machinery it used to decimate the M.D.C. and drive Mr. Tsvangirai out of the 2008 presidential runoff, according to officials in ZANU-PF and the security services, as well as human rights groups.

“That we can’t win a fair election is not a secret,” said a senior ZANU-PF official.

Speaking anonymously to discuss ZANU-PF’s confidential election strategy, the official confirmed that the party was engineering the arrests of M.D.C. lawmakers in hopes of driving them out of the government.

Further confirmation came from a senior army officer critical of the violence. He said Mr. Mugabe’s senior lieutenants decided months ago to deploy army officers, on paid leave, to manage the ZANU-PF youth militia and war veterans who assault and harass M.D.C. supporters in rural areas.

“What was curious is that most of the people who were appointed are the ones who ran the violent campaign in 2008,” the officer said.

Mr. Mugabe’s spokesman, George Charamba, rejected the claim, saying senior military leaders like Air Vice Marshal Henry Muchena of the Zimbabwe Air Force had resigned their positions to help run the election effort as a patriotic duty, not to orchestrate violence.

“The time has come to save the revolution again,” Mr. Charamba said.

Volunteers who track cases of intimidation and assault for the Zimbabwe Peace Project, a nonprofit group, have recently spotted army deployments in rural areas of many provinces, said the group’s leader, Jestina Mukoko.

“We seem to be revving up for an election,” she said.

Ms. Mukoko was abducted by intelligence agents on Dec. 3, 2008, after her organization documented the violence that stained that year’s election campaign. Two men took turns beating the soles of her feet with truncheons, she said.

Hilton Chironga, a ward-level M.D.C. organizer, is also continuing his political work, despite past attacks. Mr. Chironga recalled the morning of June 20, 2008, when a ZANU-PF mob surrounded the yard of his family’s homestead, shot him in the arm and leg and killed his brother Gibbs, a newly elected M.D.C. ward councilor.

An affidavit Mr. Chironga signed at the time listed 61 people he recognized in the mob, including two ZANU-PF members of Parliament. Not one has ever been arrested.

“We are still praying that sooner or later, we’ll get justice,” he said.