By Mabvuto Banda

LILONGWE, May 14 (Reuters) - Malawi has arrested two senior army officers for plotting to overthrow the government, police said on Wednesday, a day after the arrest of two opposition leaders on the same charges.

The detentions have left crisis talks between the government and the opposition on the brink of collapse, which threatens to derail vital international donor programmes.

Police spokesman Willie Mwaluka said the army head of intelligence, Brigadier General Cosgrave Mituka, and Major General Mathews Chirwa had been arrested on treason charges.

"All those arrested are supposed to appear in court on Thursday in Lilongwe," Mwaluka said.

Police said on Tuesday they had arrested opposition United Democratic Front (UDF) Secretary General Kennedy Mwakwangwala and senior UDF executive member John Chikakwiya, as well as former army commander Joseph Chimbayo and ex-Inspector General of Police Joseph Aironi.

Authorities also ordered the arrest of former President Bakili Muluzi, who is the UDF's candidate for next year's presidential election in the impoverished southern African country. Muluzi is out of the country.

President Bingu wa Mutharika has been holding talks with the opposition to end an impasse over the right of parliamentarians to switch their party allegiance -- a sensitive issue which led to a recent 5-day opposition boycott of the assembly and its temporary suspension.

The stalemate threatens to delay important debates on the country's budget and other measures required by donors.

The arrests are likely to worsen the crisis.

The Malawi Congress Party -- who together with the UDF forms a majority in parliament -- said they would withdraw from the talks with the government.

But UDF leader in parliament George Ntafu said his party was still committed to the talks.

"The president wants to finish UDF and he should know that we are not intimidated by these arrests. That's why we are still continuing with dialogue that was started to settle our dispute," Ntafu told Reuters.

Under wa Mutharika, the country of 12 million people has won praise and billions of dollars in debt relief for reforms that have steered healthy economic growth.

But political bickering has overshadowed those gains. Wa Mutharika's rule has been troubled since he took office in 2004, after winning an election marred by violent protests and opposition allegations of rigging. (Writing by Caroline Drees; Editing by Giles Elgood)

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