Hector L. Allen, former director of Vienna's Department of Public Works, has been named acting town manager, replacing Brackenridge H. Bentley, who resigned abruptly last week after serving seven years as manager of the town of 15,600.

The interim appointment of Allen, 71, was announced at Monday's Town Council meeting by Mayor Charles A. Robinson Jr. "Hector Allen is an outstanding individual, who enjoys an enormous level of acceptance among the town staff and is widely known and respected throughout the community," said Robinson.

Robinson said that Allen, who retired in 1981, will take up his new duties Jan. 25, when Bentley leaves his post, and will serve until a permanent manager can be found. Robinson said he hopes the new manager can take over by mid-April.

Bentley, 53, said he will assume "a more challenging job" as manager of another Virginia municipality at roughly his current salary of $47,820. He said he could not divulge the location of his new job, but a source in Front Royal said unofficially that he would become town manager there. The Warren County seat has a population estimated at 11,100.

Bentley said he leaves Vienna "with mixed emotions. I have a warm feeling for the mayor, the council and almost everyone in the town whom I've come in contact with. But it's best I leave."

Bentley's resignation follows a year of turmoil in the town, centering on dissension within the police department. Two police chiefs have been fired within a year.

Bentley fired Chief Vernon L. Jones without explanation in August 1983. Jones' replacement, Zed L. Childress, who had been handpicked by Bentley, was fired by the Town Council in June 1984 following reports of widespread dissatisfaction in the department. Childress has since sued the town for reinstatement.

In addition, a police sergeant sued the town in June, charging that he was wrongly disciplined after an alleged verbal indiscretion following a shooting incident in January. Current and former police officers have brought another four lawsuits.

Bentley said that despite these problems, and despite a recent citizen petition drive calling for his resignation, he had not been asked to leave by the council or the mayor. Upon resigning Nov. 28, however, he told a reporter, "I think there is a group out to get me. My departure should take some wind out of their sails."

C. Eugene Clarke, chairman of Voters for a Better Council, denied Bentley's charge that a particular group was out to get him. "He did himself in," said Clarke. "He knew it and we knew it -- and we're not the only ones who complained about his ineffectual leadership. There's a slew of problems in this town, and he was here for seven years and didn't address them. The record speaks for itself."

Clarke's organization had repeatedly criticized Bentley's management and what it believes is the Town Council's lack of leadership. Some of its members led the petition drive.

In a prepared statement read at the council meeting, Clarke said that the town's major problems were traffic, the lack of a master plan for commercial and industrial development, and the impurity and high cost of the town's drinking water.

Mayor Robinson declined to comment on Clarke's charges, but he did say at Monday's meeting that "no town manager will be perfect or will do everything right, the way it should be done . . . . A principal reason that the average tenure of town and city managers is as short as it is about four years is that it is difficult to avoid alienating people when you are on the firing line. The town manager has to make some difficult decisions . . . . Bentley has served with a great deal of dignity and professionalism during rather difficult days. I'll miss him."

Robinson said that the town has advertised for the position, offering a salary of $48,000 to $52,000. He said a search committee, composed of council members George E. Lovelace, Vincent J. Olson, Rodger W. Seeman and Donald E. Upchurch, will do the initial screening of applicants. The deadline for applications is Jan. 15.