With the primary little more than a week away, the two candidates who want to be the Democratic choice for County Council president are campaigning at full speed and exuding confidence.

Theresa M. Pierno, the District C councilwoman, is facing businessman and veteran politician Arthur H. Helton in what may be one of the most interesting local races in the Sept. 13 primary. The winner will face Republican Joanne Parrott, a two-term councilwoman from Fallston, unopposed in the primary.

Mrs. Pierno, who represents the greater Bel Air area, won her seat four years ago on a controlled-growth, anti-incumbency campaign. She followed up on her promise to monitor encroaching development by introducing a bill that would ban clear-cutting of trees by developers and by putting her mark on sediment-control legislation, the county's first rubble landfill bill and a package of adequate public facilities bills.

Elected in a grass-roots effort four years ago, the 36-year-old councilwoman says she's running a similar campaign this summer. About one-third of her $32,500 campaign budget to date has been in in-kind contributions, such as graphics and printing services and food for fund-raisers.

"I'm getting tremendous support from volunteers," she said. She said supporters have made all her election signs and vehicle advertisements, "and people are coming into the headquarters all the time asking for material to distribute."

Her modest coffers include $1,500 from the campaign fund-raising committee of council President Jeffrey D. Wilson, donated after he decided not to run for re-election. Mr. Wilson, elected on a similar controlled-growth platform in 1990, has evolved as Mrs. Pierno's mentor and chief supporter on the council.

Mr. Helton, 56, a lifelong Harford countian, raises sheep on his Churchville farm and owns two Western Auto stores, a small advertising firm, and business properties in Aberdeen and Havre de Grace. He is no stranger to politics. He served on the county's first council in the 1970s and spent two terms in the state Senate before losing his seat in 1982.

In 1990, Mr. Helton attempted to make a comeback, running for the council presidency, but was denied the nomination by Frederick J. Hatem, who lost in the general election to Republican Jeffrey Wilson.

He reported raising $54,000 for his campaign on his latest financial statement Friday. That includes $37,500 in personal loans he made to his campaign.

"I feel pretty good," he said last week. "I'm getting good response from the public. People are calling in for signs [to post] and my TV ads have been fairly effective."

Mr. Helton holds an obvious financial advantage over his opponent, and he is the obvious choice of people in the business, real estate and development communities, who see the environmentally sensitive Mrs. Pierno as a threat to their future. It appears that the councilwoman's estrangement from the development community, as much as Mr. Helton's membership in the county's developer-heavy Economic Development Commission, has led to his image as the pro-business candidate and Mrs. Pierno's as the people's candidate.

The two agree that the main issue before voters in this election will be growth management -- where, how fast and with what kind of development the county should grow.

Mrs. Pierno says growth management is "even more important now than it was four years ago." The county has been growing at a rate of about 2,000 residential units a year, she points out, far more than its public facilities can keep up with.

"We've been building a school a year and still have problems keeping up with the demand," she says. The councilwoman wants to continue to work on legislation that would require schools, roads and water and sewerage facilities to be up to par before further construction can proceed.

She says that, with a comprehensive zoning review on the council's agenda for 1995, she fears that developers will pressure the council toward rampant rezoning that would open more land in the county to builders before it is adequately equipped with public facilities.

Mr. Helton says he's not against adequate public facilities laws, but he fears that tight restrictions on landowners who intend to develop their properties could land the county in court battles over property rights.

And he thinks that a sizable share of the population favors a growing county, if it means more commercial and industrial operations that will provide jobs for residents and more tax revenue for the county.

The county's weak industrial tax base has long been a concern to the administration and council. About 75 percent of property taxes comes from residential property, and about half the working residents are employed outside the county.

Mr. Helton says the county already has land zoned for commercial and industrial use that is underutilized and needs to be upgraded -- or put on an accelerated schedule to get public facilities -- to render it more marketable.

"This county needs to articulate an economic development statement that would guide the master plan," he says. "It would say what kind of business and industry we want to attract. It would be our mission statement. Right now our statement is, 'If you will come, we will take you.' "

Both candidates are canvassing door to door, appearing at bull roasts and attending candidates nights that tend to attract more candidates than voters.

Mr. Helton says he's getting support from every part of the county, and his name is widely recognized. He has spent nearly $20,000 on cable television and newspaper ads, and has many campaign signs posted throughout the county.

He's also invested in direct mail and telephone campaigns, and says he has visited 65 percent to 70 percent of the homes in the county.

Mrs. Pierno, an energetic representative of Harford's newer residents -- she moved to the county in 1985 -- acknowledges she is more widely recognized in the heavily populated areas around Bel Air than in the outer reaches of the county.

"But we're out there every night, knocking on doors," she said.

The winner will face District B Councilwoman Parrott in November.

One of only two incumbents re-elected to the council in 1990, Mrs. Parrott is counting on eight years' experience there to carry her some distance. She has been actively campaigning since spring, she says, among veterans, seniors, farmers, community groups and the business people, who, with county firefighters, may prove her strongest supporters.

She has gained a reputation in recent years as being pro-development, especially during entanglements with Mr. Wilson and Mrs. Pierno over legislation that would affect the business community.

The Republican councilwoman says the County Council "has strayed from its true course" as the legislative branch of local government. "Some of my colleagues want to be co-county executives," she says.

"I don't think the point of the council is to agitate. I think it's (( important for the president to create unity," she said.