John G. Milliken, the only Northern Virginia Democrat to survive last month's Republican landslides, will be elected chairman of the Arlington County Board on Jan. 1, the board's current chairman, Ellen M. Bozman, announced yesterday.

Milliken, who was reelected Nov. 6 with a decisive victory over Republican Peter Espada, will serve as chairman for one year.

An aide to former representative Joseph L. Fisher of Arlington and a member of a Washington law firm with Walter F. Mondale, Milliken is to leave the position of chairman of the Metro transit board next month.

Mary Margaret Whipple, one of the four Democrats on the five-member Arlington County Board, will be elected vice chairman, Bozman said.

Although the board's Democratic majority will not make a formal statement of its priorities for 1985 until its Jan. 1 organizational meeting, several board members said yesterday that one of their major concerns will be the impact on Arlington of proposed cuts in the federal budget.

"We're back where we were in 1980 and 1981, when all these Draconian cuts were coming out," Milliken said.

Board members cited a recent memo from County Manager Larry Brown saying that, if suggested federal cutbacks are enacted, Arlington could lose a minimum of $803,700 in fiscal 1986 and $4.8 million the following year.

The cuts would be largely in community development block grants programs, revenue sharing and legal services for the poor, they said.

Dealing with continuing concerns such as housing -- "probably one of the most intractable problems the county faces today," said board member Albert C. Eisenberg -- will be difficult if the cuts are approved, several board members said.

"The federal government likes to pass us the buck but not the dollar," Eisenberg said.

With the likelihood of cutbacks in mind, the board will concentrate next year on long-range fiscal planning, an effort started two years ago, said Bozman.

"I expect us to begin this year a really more organized discussion of long-range fiscal policy," she said.

The board also will focus on comprehensive community improvement programs, drawing development plans for sections of Arlington larger than those the board has approved around Metro stations, Bozman said.

"The comprehensive improvement notion is something we will want to continue and refine and define -- these are things that directly affect the quality of life in Arlington," Milliken said.

In addition, said Bozman, the board will continue its "in-depth look at county government, department by department."

That process, which already has included examinations of the fire department and the Department of Human Resources, "has been very useful," she said.