BANGKOK — Plans by the Malaysian government to shut down the troubled state fund at the heart of a multinational investigation could saddle the government with billions of dollars in debt and may be a first step toward a government bailout, opposition leaders said.

The government announced plans this week to close the fund, which was created by Prime Minister Najib Razak and is suspected of being the source of hundreds of millions of dollars deposited in his personal bank accounts.

The Finance Ministry said on Wednesday that it would absorb the fund, 1Malaysia Development Berhad. The ministry, which Mr. Najib oversees in his capacity as the country’s finance minister, will take over 1MDB’s remaining assets.

Critics are concerned that the ministry will also assume the fund’s estimated $6.75 billion debt, setting the stage for a government bailout.