With balloons labeled "rising prices" soaring into the sky and television cameras grinding, a handful of Washington residents held a sidewalk press conference in front of the Washington Gas Light Co. last week in protest against "the big rip-off" by utility companies.

The protesters, about a dozen in number, claimed to represent 140 organizations in the District, Maryland and Virginia, which, they said, have joined together as the Metropolitan Area Coalition on the Energy Crisis.

John M. Thorton of the District, chairperson of the Coalition, said the group formed "to defend ourselves against the prices of utility companies" and referred to the new system charge levied by WGL as a "one-and-a-half million dollar rip-off."

Eleanor Cortez, who said she was from the "Takoma Park-Langley Park area" and represented a "suburban Maryland coalition against inflation," called for "lifeline rates" under which poor people would receive subsistence levels of utility services whether they could pay for them or not. She also said utility companies should stop advertising and not take out country club memberships for executives.

But the main complaint of the Coalition was against the system charge, granted to WGL by the Public Service Commissions of the District and Maryland.

According to regulatory agency and company spokesmen, the system charge plan is new to this area but has attracted favorable attention from other locales.

Under the plan, customers pay a basic, fixed monthly charge no matter how much gas they use or whether they use any at all. For D.C. residences, it is $8 per month nine months of the year. Maryland customers pay the $8 every month, but have a lower-per-therm-of-gas rate. The rate in Maryland is 20.73 cents. In D.C. it is 21 cents. There are several variations of this basic formula for non-heating users of gas and for business and industrial customers.

According to the spokesmen, the basic monthly system charge is not an "extra" charge and if it were eliminated the same amount of money would be collected from customers over a year through higher rates.

The reason WGL wants it, the spokesmen said, is to guarantee a regular monthly income independent of gas consumption in order to pay fixed operation and administration cost.

The regulators and the company believe it is good for consumers, too, because it spreads the annual cost of gas service more evenly over the year rather than concentrating it in the heavy usage winter months.

However, the organizations of consumers seem to disagree and to regard the system charge as an unfair boon to the WGL. A campaign against it also has been started by the Maryland Action Coalition, an organization claiming to represent 75 Maryland groups and which is in the midst of an effort to gain pledges from WGL customers to withold payment of part of their gas bills in protest.

Last week's Coalition leaders, who said they represented labor, civic, church, senior citizen and public interest groups, announced a "People's Convention on the Energy Crisis" to be held May 7 from 9:30 a.m. to 2 p.m. at the New York Avenue Presbyterian Church, 1313 New York Ave. NW.

Previously, the Maryland Public Service Commission said it would sponsor an "informal consumer conference" in the Montgomery County Council chambers in the County Office Building in Rockville at 8 p.m. on May 24.