Angry gasoline station owners and a major oil company representative have launched an old-fashioned, hardball lobbying campaign against Mayor Marion Barry's proposed 6 percent tax on gasoline.

The owners, all city-based members of the Greater Washington-Maryland Service Station Association, roamed the corridors of the District Building yesterday and Wednesday in their blue and pinstriped workshirts, button-holing City Council members, jawboning council aides and meeting briefly with Mayor Barry. They warned that the tax, scheduled for final vote by the council next week, would force city motorists to seek cheaper gasoline in Maryland.

And Exxon Corporation lobbyist Dwight W. Tate, who accompanied the owners on their rounds yesterday, told council members and the mayor that Exxon may reconsider its $10 million investment for several new service stations in the District if the tax passes.

"That investment was made based on estimates of gallons sold," Tate told an aide to Councilman John Wilson (D-Ward 2). "It becomes quite apparent that if this tax is passed, that investment is not warranted any longer."

It was the kind of play-for-keeps lobbying the City Council hasn't seen on an issue in months. While some council members stiffly resisted the campaign, there were signs that some compromising on the tax may occur.

Wilson and some other council members are said to be considering reducing the 6 percent tax -- perhaps by as much as one-half -- and then making up the lost revenue by taxing some of the service in gas stations, like labor for car repair. This is a plan the owners say they can live with.

Other Council members expressed annoyance at the lobbying effort.

"Where the hell were they in March, April, May and June?" said Council member Betty Ann Kane (D-At-Large). "It's very hard to make a change now. The budget's already been sent down."

Also, said Kane, "the money that they're spending for their (newspaper) ads they ought to spend to take out an open letter to the citizens of Maryland asking them to tell their representatives to support the full federal payment," for the District of Columbia.

The 6 percent gasoline tax is proposed as part of the mayor's package of new and increased taxes designed to raise $20.2 million before Sept. 30 to help the city erase its deficit. The gas tax was estimated to raise $2.33 million in new revenue this year, assuming it is in place by July 1.

Coundil is scheduled to vote on the tax Tuesday as an emergency measure to go into effect Aug. 1. If any amendment is added on Tuesday, such as a reduction in the size of the gasoline tax, the entire measure would have to be delayed for an additional two weeks, further delaying implementation of the entire package.

Carolyn Smith director of the D.C. Department of Finance and Revenue, has said the city will lose $3.4 million for each month past July 1 that the tax plan is not in effect.

In an effort to stop the gasoline tax from passing next week, the service station owners bought a full page advertisement in Wednesday's District section of the Washington Star, estimated to cost $5,562, and another in yesterday's Washington Post for $1,822. The ads tell city motorists to write the mayor and the members of council in protest against the tax.

In addition, owners have been collecting signatures from their customers on protest petitions, which they will present to the council and the mayor next week. They also plan another meeting with Barry on Monday.

The owners claim that the 6 percent tax, estimated to add up to about eight cents per gallon at present prices, will actually cost the District more money in lost sales to the suburban Maryland stations that have generally lower prices.

"It's going to cost the District government lost taxes," Exxon's Tate said. "Not only are you going to lose taxes, you are going to lose many dealers who are paying license fees, and employing people."