The U.S. attorney's office here began an investigation yesterday into allegations that officials of P. I. Properties Inc. misused or stole at least $600,000 from the U.S. government and low-income tenants over a four-year period.

Grand jury subpoenas will be issued immediately for records and witnesses concerning the alleged theft of government funds,it was learned yesterday.

Possible crimes being investigated include conspiracy to defraud the United States, mail fraud, false statements to government agencies and obstruction of justice.

In addition, the FBI has begun investigating allegations that a witness to the alleged crimes was threatened, sources said.

The witness, former P. I. bookkeeper Zellene Laney, said she received the threat Thrusday in a telephone call that she reported that night to The Washington Post. On Friday The Post informed the FBI about the threat and the agency opened its investigation.

A series that began in The Post yesterday detailed allegations against three officials of P. I. Properties Inc., a nonprofit real estate spinoff from Youth Pride Inc., a 12-Year-old black, self-help organization here.

The officials, including Mary Treadwell, Mayor Marion Barry's former wife, systematically siphoned the money from the operation of the federally funded Clifton Terrace Apartments complex and from two privately owned projects, The Post story said. The other tow P. I. officials involved were Robert E. Lee jr., the firm's former general manager, and Joan Booth, Treadwell's sister, who acted as project manager for the apartment complex.

No allegations have implicated Mayor Barry.

The fraud division of the U.S. attorney's office here has been aware for about two months of an audit of P. I. being conducted by the U.S. Department of Hosing and Urban Development, it was learned. However, that audit reportedly has focused only on examination of records and did not involve any allegations by witnesses to the alleged theft.

It is known that U.S. Attorney Carl S. Rauh and Assistant U.S. Attorney John T. Kotelly, deputy chief of the fraud division, discussed the allegations against P. I. Properties after the first article in The Post's series was published yesterday and decided to open a federal grand jury investigation. Neither would comment directly about their plans.

Laney, the former P. I. bookkeeper, said the threat against her Thursday night was the second she has received concerning her involvement in P. I. Properties.

Earlier Laney had told two Post reporters that shortly before she quit her job with P. I. Properties she was confronted by a man as she sat outside the building with her infant daughter.

She said the man who approached her knelt in front of her and spoke directly to the infant, saying, "baby, wouldn't it be too bad if you didn't have a mama no more?"

She reported that threat to a Clifton Terrace security officer, who later recalled the conversation with Laney. The Security officer said the man had been carrying a sawed-off shotgun at the time the threat was made.

Laney, who no longer lives in the Washington area, said she was called Thursday night by a person whose voice she knew and was reminded "that i have kids" when she confirmed she had been talking with Post reporters about P. I. Properties.

The Post informed the FBI and the major crimes division of the U.S. attorney's office here after Laney told reporters about the Telephone call.

Laney said yesterday that the FBI came to see her and talked with her for about an hour Friday night, offering to protect her if she felt it was necessary.