Loudoun County, following Fairfax County's example, yesterday banned sale of throwaway containers, effective Jan. 1.

The Loudoun ban, passed unanimously, goes further than the one that has been in effect in Fairfax since Sept. 1 by including beer containers as well as containers of carbonated soft drinks. A Montgomery County law, recently upheld by the Maryland Court of Appeals, also will require refunds on beer containers when it goes into effect in several months following further proceedings in a lower court.

A major argument of the soft-drink industry has been that requiring return of soft-drink containers for refunds would fail to solve the roadside litter problem that is the major target of the legislation.

Previous attempts to require refunds on beer containers have been knocked down in Virginia on grounds that alcoholic beverages are the exclusive domain of the State Alcoholic Beverage Control Board. Loudoun County Attorney Stephen Robin contends that his ordinance seeks only to regulate litter and that the ABC regulates aspects other than litter.

Loudoun Supervisor James P. Brownell said of the ordinance that "from the rumors I've been hearing I think we'll be defending it (in court)."

Robin's ordinance includes a "severability clause," which, states that if any part is found unconstitutional or invalid the remaining portions will not be affected.

The ordinance requires that beverage containers have a refund value of at least 5 cents and that they be marked for sale in Loudoun County. It also requires that dealers accept containers from customers and pay cash refunds. Violators can be fined $1,000 and jailed for 30 days.

In Fairfax County the law bans sale of pop-top soft-drink cans. In Loudoun, pop-top soft-drink and beer cans may be sold when the law goes into effect if a refund is given for their return. The supervisors said state legislation will bar pop-tops effective Jan. 1, 1979.

Loudoun County adopted its first throw-away ban in 1971 but that law was immediately challenged by the beverage industry and found unconstitutionally vague. Robin said yesterday he believes that problem has been solved and he is prepared to defend the ordinance in court.

The action by Loudoun County could spur similar measures by other Virginia jurisdictions. A copy of the Loudoun ordinance has been sent to each board of supervisors in the state and board members from Caroline County were present yesterday to praise the Loudoun supervisors for their action.