The Manassas City Council is expected this week to name longtime public works director Clyde Wimmer to the newly created post of assistant city manager, according to council member James Payne.

Wimmer served as acting city manager twice, once when the manager retired and the second time when the manager resigned after serving one year. Wimmer was one of 115 candidates for the job when the council advertised the position in November. Officials said the post became necessary because of the amount of work generated by the city's growth. Wimmer, who has served Manassas for 15 years, will probably be given responsibility for public works in his new position, officials said.

"Nobody knows water, sewers, electricity and roads like Clyde," said council member Maury Gerson. Jail Board Insurance Is at Issue

* A joint committee of Manassas City and Prince William County officials has agreed to consider a self-insurance plan for the Prince William/Manassas regional jail board, county attorney John Foote said.

The council met to consider several options last week after the two jurisdictions were told that the liability insurance for the jail board would be canceled one minute after midnight July 1. The expiration date was moved to July 31 to give the city and county time to find another carrier, but was moved again to Aug. 16 when it was discovered that state law required 45 days notice for insurance cancellation.

Foote said the self-insurance plan would require that the city and the county provide the same percentage for the insurance reserves as they do for operation and maintenance of the jails, which is 93 percent for the county and 7 percent for the city. Although Manassas Park also uses the jail, it is doubtful that city officials will enter into the insurance plan. Instead, Manassas Park's cost of operation and maintenance will be raised slightly, said Foote.

The county board of supervisors is expected to vote on the new policy at its Aug. 5 meeting. If the policy is approved, the jail board will join the county's police department, fire marshal, the juvenile detention home, the commonwealth attorney and other law enforcement officials and agencies permitted to use the county's self-insurance trust fund. The board on July 1 adopted a resolution permitting such use after the liability insurance premium for those officials and agencies was increased by 41.9 percent. Manassas Battle Commemorated

* The 125th Anniversary of the First Battle of Manassas will be commemorated this weekend with a series of special events, including concerts by the U.S. Army Band, artillery demonstrations, hot-air balloons, horse-drawn carriage rides and a civil war seminar.

Prince William County Tourism Director Bernadette Plunkett said the events will be held at the Manassas National Battlefield Park on Route 234, near the campus of Northern Virginia Community College, Ben Lomond Park in Manassas, the Manassas Holiday Inn and in Old Town Manassas. In Old Town, the emphasis will be on the First National Jubilee of Peace held 50 years after the battle when the veterans of both armies met in Manassas in a gesture of peace and friendship.

The Manassas Performing and Fine Arts Center will participate in the peace jubilee by providing 40 "maidens" like those who sang the hymn "United" at the first jubilee. But according to center director Bea Bright, the modern maidens will perform instrumentally as well as vocally. For information call 368-FINE.

In addition, the American Civil War Commemorative Committee will stage a reenactment of the battle at 1 p.m. Sunday at a 500-acre site off Rte. 28 in western Fairfax County. Tickets for that event must be purchased in advance. For information call 825-8628. For information on activities sponsored by Manassas or Prince William County, call 335-6680 or toll free from Washington 631-1480. Ball Tournament Starts Sunday

* The Dumfries/Triangle/Quantico Little League and the Virginia District 9 Little League will sponsor a 1986 Senior League softball state championship tournament beginning Sunday. The tournament will be held at the Davis Ford Road Stadium. For information call tournament director John Hambrick at 670-5335. Pr. William Officers Promoted

* The four Prince William County police officers promoted last week included the first female police officer to attain the rank of corporal in the county. Promoted to sergeant were Gerald Jones and Ronald Sullins; Jeanette Williams and Raymond Colgan were promoted to corporal. The county hired its first female police officer in 1974; currently there are 22 female officers on the force, a spokesman said. School Boards Elect Leaders

* The school boards of Prince William and Loudoun County last week elected new chairmen and vice chairmen to serve one-year terms.

In Prince William, Occoquan representatives Ilona Salmon was chosen chairman, and Patricia Cusey, appointed last year to fill the Gainesville post, was elected vice chairman. Salmon replaced Gerard Cleary, who has often been under fire in recent years for several controversial decisions. Cleary had served as chairman since 1980 and will remain on the board representing the Woodbridge district.

Two women also took over the top posts in Loudoun. Leesburg representative Betty Poehlman is the new chairman; Catoctin representatives Bonnie Epling is vice chairman. Poehlman replaces Warren Braham, who did not seek reappointment to the board because of increased professional responsibilities. Poehlman's post will be a difficult one because four members of the school board began their terms last month, a spokesman said. Energy Improvements In Store

* Residents of an apartment complex for low- and moderate-income families in Dumfries will receive new heating and cooling systems and insulated sliding glass doors. The changes are designed to cut energy costs and improve heating and cooling in the 14 one-bedroom apartments, said Virginia Bentson, spokeswoman for the Prince William County Department of Social Services.

Dumfries Heights apartment owner Gino Orsini will pay for half of the rehabilitation work, with the other half of the more than $30,000 tab being picked up by the Virginia Housing Development Authority. Orsini has also agreed to participate in a federal housing program that ensures the cost of the repairs will not be passed on to tenants in the form of higher rent, Bentson said. Apartment owners and tenants may call the Department of Social Services at 369-8670 for more information on these housing programs. Vietnam Memorial Moves Ahead

* A design for the Loudoun County Vietnam Memorial to be erected on the courthouse lawn in Leesburg has been approved by Circuit Court Judges Carlton Penn and Thomas Horne and the Board of Supervisors.

According to memorial committee chairman Ben Lawrence, the memorial will consist of a stone 10 feet by 12 feet and 2 feet thick that will have the names of soldiers from Loudoun who died in the Vietnam War engraved either in the stone itself or on the bronze plaque attached to it. The memorial, which has been in the planning stages for nearly three years, was designed by local architects Ballinger and LaRock. It will cost between $50,000 and $100,000 and will be paid for with private donations, Lawrence said. The three memorial subcommittees will meet soon to work out details of design, landscaping and fund raising, he said.

Lawrence, who also is chairman of the 1986 Keep Loudoun Beautiful campaign, said the state highway department has agreed to erect 13 "no littering" signs in the county. Areas to receive the signs include the Rte. 15 and Rte. 50 intersection, White's Ferry, Balls Bluff, a site near the Federal Aviation Administration Center east of Leesburg and sites east and west of Purcellville. Loudoun Hospital Golf Classic Set

* Officials of Loudoun's Memorial Hospital are urging golfers interested in participating in the hospital's annual golf classic slated for Friday, July 25, to register no later than Sunday.

There is a $100 entry fee for the charity event to be held at the Westpark Hotel and Golf Club; a reception and dinner will be held at 7 p.m. at Morven Park in Leesburg. According to a spokesman, golfers will compete for nearly $2,500 in prizes. More than 120 persons have registered. The public is invited to attend the dinner, for which there is a $30 fee. Advance registration is required. Call 777-3848 for information.

The hospital's Ladies Board Auxiliary recently donated $19,000 to the hospital board for a CP scanner. The gift represented the group's fourth payment on a $75,000 pledge for the diagnostic equipment. According to auxiliary president Kaye Stowers, there is a pledge balance of $5,500. The Ladies Board is still accepting donations for its annual sale at the 4-H fair grounds Saturday and Sunday. To donate clothing, furniture, appliances or other items, call 777-7164. The money will also be used to buy hospital equipment, spokeswoman Irene Cromer said. Leesburg Plans Musical Evening

* John Roberts and Tony Barrand will present an English Music Hall evening at 7 p.m. Sunday on the steps of the Old Courthouse in Leesburg. The performance will be the fifth of a series of 10 special events in the Bluemont Concert series. Series director Peter Dunning said the two entertainers will offer song, tales, humorous monologues, dances and tunes from the British folk tradition. If weather does not permit an outdoor performance, the concert will be held at the Leesburg Methodist Church, 33 Market St. An announcement on the decision to move inside can be heard on WAGE Radio at 5 p.m. Middleburg Water Use Declines

* Outside water usage has decreased more than 30 percent in Middleburg since the Town Council recently imposed a moratorium on lawn watering and car washing during the prolonged drought, Mayor Loyal McMillan said. Usage has gone from 105,000 gallons daily to 70,000 gallons daily, he said. Violators of the moratorium could be fined as much as $500, but officials do not expect to have to enforce the ordinance. "Everybody is cooperating tremendously," McMillan said. Polo Games Set in Middleburg

* Polo games will be held at 3 p.m. Sunday and next Sunday, July 27, at the polo grounds west of Middleburg on Rte. 50. For information call 777-1403 or 777-9243. Lovettsville Applies for Grant

* The Lovettsville Town Council has applied to the Virginia Water Project for a $5,000 grant to dig a new well at the north end of town.

Application for the grant has been delayed because town officials had been told that personal information regarding the incomes of residents must be provided in order to qualify. Council member Thomas Cane said that an inquiry to the Northern Virginia Planning Commission resulted in the assurance that, because the commission recently granted the town more than $643,000 to rehabilitate the town's sewer system without the personal information, the Virginia Water Project would probably grant the funds for the well without it.

"What they want is proof that the well will serve low- and moderate- income residents," Cane said. "Since we applied, the Virginia Water Project has been encouraging." Town Imposes Site Moratorium

* The Purcellville Town Council last week approved a moratorium on accepting site plans for subdivisions that have not been previously approved for a water tap. The moratorium was necessary because all available water taps are reserved and the town has been inundated with site plans, Town Manager William Dennis said. Plans that have already been accepted will be kept "on hold" and the door "left open" for more site plans in the future, he said. The town may construct a retention basin to increase its water supply. Purcellville Fair Begins Today

* Today from 10:30 a.m. to 3:30 p.m., a World Fun Fair will be held at the Purcellville Community Center. The event will feature a variety show, dancing, truck rides and a water slide. Admission is free. For information call 338-4122. Round Hill Council Adopts

* Budget The Round Hill Town Council last week approved a budget of more than $175,000. The largest budget item, Mayor Jeff Wolford said, is $41,500 for operation and maintenance of the town's sewer system.

Although Round Hill has often had to impose water use restrictions during severe droughts, Wolford said the town's water supply is still sufficient. "My wife and I took a ride up the Blue Ridge mountain last week, and the water level in the reservoir is just one foot below the overflow mark," he said. "I don't know how we're doing it but I'm glad." At its meeting at 8 p.m. today, the town council may consider putting restrictions on water use in the event of a continued drought.