A Montgomery County grand jury has begun an investigation into allegations of bribes and questionable purchasing practices by the county Department of Liquor Control, sources close to the investigation said yesterday.

The grand jury, which is scheduled to meet on Thursday, subpoenaed documents relating to the liquor department last week. At least two persons received subpoenas for documents: Leonard I. Colodny, the former consultant on the Department of Liquor Control who was hired and then fired by County Executive Charles W. Gilchrist, and Andrew Mansinne, a county official who until last month was going to determine the merit of allegations that had been made by Colodny about the department.

"They are looking at everything, even from years ago," said one source close to the investigation.

The subpoenas issued by the grand jury follow months of newspaper reports about questionable practices by the department of liquor control, the agency that purchases all liquor, wine and beer that is sold in the county. In addition to acting as the sole wholesaler of liquor in the county, the department also retails liquor in its 20 county-owned stores.

According to one source, the following are among the allegations that the grand jury expects to examine:

That Ken Dragon, a former deputy director of the county department of liquor control, accepted money and tickets to a baseball game from officials of Schenley Industries, Inc., a New York-based liquor firm. f

That Earl Buscher, a Schenley salesman to the county, gave county officials free bottles of Schenley liquor each week.

That the county Department of Liquor Control purchases an inordinantly large amount of liquor from Schenley as a result of county officials' close ties with Schenley officials.

For the last two months the Montgomery County Council has been conducting its own investigation into allegations of favoritism in purchasing practices by the county Department of Liquor Council. The allegations were made in an article in the Washington Post and later were amplified by Colodny, the liquor consultant hired by Gilchrist.

Council members asked Mansinne, director of the council's office on legislative oversight, to investigate the department after Colodny was fired by Gilchrist. Last month, however, the council removed Mansinne from the investigation after he said that he had about a dozen business and social meetings with Charles Buscher, a former Schenley executive who was a key figure in the investigation.

The council does not plan to hire an investigator to replace Mansinne, council president R. Scott Fosler said yesterday. Instead, the council will decide whether there is any merit to the allegations, after an accounting firm, Touche, Ross and Co., examines the Department of Liquor Control's books.

Several weeks ago, Fosler had asked three council members -- Ruth Spector, Esther Gelman and Neal Potter -- to consider choosing an investigator to replace Mansinne.

The committee met twice, but on Thursday Fosler reportedly told the council members that there was no need for them to meet anymore and that the entire council would study the allegations.

At yesterday's council meeting, Fosler denied that he had ever formed such a committee although two council members, Gelman and Spector, said they attended its meetings. Fosler would not say why he had decided not to replace Mansinne.

Meanwhile, the county personnel board is looking into allegations that the merit system was tampered with in two instances: when Frank Orifici, a former Schenley salesman to the county, was made deputy director of the Department of Liquor Control in April, and when Colodny allegedly was offered a merit job in the county liquor department by County Executive Charles Gilchrist in January.