ATLANTA (AP) _ Atlanta's rapid transit system is beckoning to booming suburban Gwinnett County, but some voters there want to derail the expansion because of fears that blacks from the city will stream out on buses and trains.

Others say they simply don't want to pay for it.

Gwinnett County voters decide Nov. 6 whether to bring the Metropolitan Atlanta Rapid Transit Authority into the county in exchange for a 1 percent sales tax.

County Commissioner W.J. Dodd said his constituents oppose the idea, and he predicted it would fail.

''One of the worst fears is bringing people out of Atlanta, the minorities,'' he said. Dodd refused to say where he stands on the expansion.

Blacks and other minorities make up only 6.4 percent of Gwinnett's 355,000 residents. Blacks make up 66 percent of Atlanta's 425,000 people.

Voters in the northeastern Atlanta suburb rejected mass transit service in 1971. That same year, Fulton and DeKalb counties - which make up Atlanta - became the first in the nation to pay voluntarily for a mass transit system.

The sales tax they approved has not kept pace with MARTA's expenses, though. The system in July raised bus and train fares 15 cents to $1 rather than cut service.

MARTA, the South's first mass transit system, now transports 280,000 bus riders and 220,000 rail passengers daily. The rail line stretches in four directions from downtown Atlanta to Fulton and DeKalb suburbs and to Hartsfield Atlanta International Airport.

Residents of Gwinnett County, whose population has quintupled since 1971, depend on their cars - 311,000 of them. Traffic is bumper-to-bumper from Gwinnett into downtown Atlanta most weekdays.

MARTA officials estimate mass transit could take 25,000 cars off the county's roads, and ridership in Gwinnett could reach 60,000 by the year 2010.

Opponents argue that the masses would finance the expansion but that only businesses trying to attract low-wage workers would benefit. The plan's foes have taken their campaign to grocery stores and malls, handing out Ban MARTA stickers.

Supporters of the plan have put up signs on Interstate 85 into Gwinnett County that read, ''Gwinnett's Future is Riding on MARTA.'' Radio spots tout the benefits of public transportation.

''Some people have said they oppose MARTA because they are concerned about crime and a decrease in their property values,'' said Richard Myrick, a Gwinnett businessman leading the expansion effort. Myrick and others are trying to assure residents that public transportation won't ruin their neighborhoods.

If voters approve, MARTA will spend $681 million to extend a rail line 10.8 miles toward Gwinnett Place Mall in Duluth. The line would be completed by 1998.

Gwinnett County residents would pay a 1 percent sales tax until the year 2032 and a 1.5 percent sales tax for the next eight years until the contract expired in 2040. The current sales tax in Gwinnett County is 5 percent.

A Gwinnett Daily News poll last month found that 60 percent of voters surveyed opposed the sales tax. Twenty-six percent of the 500 voters said they would foot the bill; the remainder were undecided. The newspaper gave no margin of error for the poll.

Anna Roupe said she would vote against the expansion.

''The people of Gwinnett County can't afford it,'' she said. ''As far as I'm concerned, for me, it's my pocketbook. There is no other issue.''

Joe Lupton of Snellville said there is another issue for county residents: crime. ''I would hasten to say they fear for their lives,'' he said.

Gwinnett County Commission Chairman Lillian Webb, the only commissioner who has voiced support for the expansion, lamented that many people see it as a racial issue.

''Some of them have said, ''We don't want those people out here.' It upsets me. The other races, other ethnic groups contribute to our cultural diversity,'' she said.