ANNAPOLIS -- When Anne Arundel County's 172,000 voters return to the polls Sept. 11, they will be confronted with the most dizzying array of choices they have had in at least eight years and possibly since the county adopted a charter form of government in the 1960s.

In addition to filling a vacancy in the county executive's office, voters in Arundel will be confronted with three open County Council seats, a rare contested state's attorney's race, seven would-be sheriffs, a crowded camp of candidates vying to represent Annapolis in the House of Delegates, and a heated contest for state Senate in north Arundel.

The reason for the wide selection, besides attrition, is that county Republicans are fielding their most complete group of candidates in years, according to political observers. Buoyed by voter registration, increases that have narrowed the gap between Democratic and Republican voters to a 1.5 to 1 ratio, local GOP leaders have worked hard to provide opposition in nearly every race. Just six years ago, the ratio was more than 2 to 1.

The recruitment drive has worked so well, in fact, that there will be Republican primaries in six of the seven council contests, something that until now has been unheard of here. There will also be six Democratic primaries for council.

"There are probably a lot more candidates than you usually see. It's a good sign," said state Sen. John A. Cade (R-Anne Arundel). "There were a lot of people who, when they came here, were told to register Democrat because that was the only way they could really participate. That's not true anymore."

With County Executive James Lighthizer (D) forbidden by law to seek a third term, much of the excitement in both camps has focused on selecting his successor.

The four Democrats who have entered the race to succeed Lighthizer are: County Council members Michael F. Gilligan, 47, (D-Glen Burnie) and Theodore J. Sophocleus, 51, (D -- Linthicum); former Annapolis mayor Dennis M. Callahan, 47, and former state delegate Patricia Aiken, 61.

GOP leaders are particularly optimistic they will win back the county executive's office now that the party has united around the candidacy of former House minority leader Robert R. Neall.

Last month, Del. John R. Leopold (R-Anne Arundel) decided to run for state Senate against incumbent Philip Jimeno rather than face Neall in the primary. On Monday, William J. Steiner, a political unknown who has not voted in the past four elections, entered the race as a Republican.

Neall, 41, so far has raised more in campaign contributions than all of the four Democratic contenders. Some observers believe Neall also has the behind-the-scenes support of several prominent Democrats, including Lighthizer, on whose transition team Neall served, and Gov. William Donald Schaefer, for whom Neall served as drug policy coordinator.

"It is going back to Neall," said Circuit Court Judge Warren Duckett Jr., considered the dean of Arundel's Democratic politics until his appointment to the bench in 1988. "I was at his {$500-a-head} fund-raiser last month, and I saw more Democrats there than anyone else. He has a style and sophistication about him that the other candidates just don't have."

Democratic leaders, however, are ready to concede nothing. They point to Neall's tense history with local environmentalists and teachers -- two of the more powerful lobbying groups -- and see a politician who is beatable. Sophocleus and Gilligan are considered the early favorites among the Democrats, although some observers believe that Callahan could make a strong showing since the two council members share the same north county base and may divide the vote there.

"I don't think the county executive's race is there for Bobby Neall to pick off," said Gilda Atas, chairman of the county Democratic Central Committee. "Once the primary is over and we know who the candidate is, I think you'll see the Democrats will really unite behind that candidate."

With Gilligan and Sophocelus leaving the council after eight years each to run for executive, their seats are up for grabs. In Sophocleus's Linthicum district, Democrats George F. Bachman, John Stokes Sr. and August L. Lundquist will square off in the primary, although observers have given the edge to Bachman, who held the seat for 18 years until he stepped down to run for county executive in 1982. James W. Sakers and Gerald P. Starr are the Republicans in that race.

In the race to represent Glen Burnie and succeed Gilligan, there are five Democrats: George F. Johnson III, Joseph Procaccini, Charles M. Eckman, Daniel Klosterman and Edward Middlebrooks. The Republicans in that race are Michael J. Serabian, Ernest C. Michaelson and Sharyl L. Wolfe.

Of the open council seats, the most excitement has been generated around the Severna Park district represented by Democrat Carole Baker, who is leaving politics after eight years on the council. Local Republicans consider the candidacy of Diane R. Evans, a former Neall aide who ran against Baker in 1982, their best hope for achieving their first seat on the County Council in 20 years, although another Republican candidate, Andrew L. Buettner, filed this week to challenge Evans in the primary.

Eight Democrats -- Linda Gilligan (Council member Gilligan's sister-in-law), Edward Doyas, Robert J. Cancelliere, A. Michael Bohle, Michael L. May, John W. Russell, Eugene F. White and Mary K. Harris -- are vying for the nomination for Baker's seat.

All four incumbents on the council will have opponents as well. Democratic council member David G. Boschert, of Crownsville, will face Edwin Bell Jr. in the primary, but there is no Republican in that race. Council Chairman Virginia P. Clagett (D-West River), who represents the southern part of the county, will face Patricia J. O'Brien in the Democratic primary. Republicans John J. Klocko III and William Alan Boehm will square off in the primary to run against Clagett.

Council member Maureen Lamb, of Annapolis, has no Democratic opposition. Two Republicans, J. Patrick Ogle and Glenwood Gibbs, are in the primary to challenge Lamb. In the Pasadena area, four candidates -- Peter Cooper, Thomas C. Henderson, William R. Jahnigen and Susan E. Pogue -- have challenged County Council member Edward C. Ahern in the Democratic primary. George J. Acton and Carl G. Holland have filed as Republicans.

Voters will be faced with a novelty in another countywide race -- the first two-candidate campaign for state's attorney in 16 years. Timothy D. Murnane, a county public defender until last week, has announced he will run as a Republican against Democrat Frank R. Weathersbee, who was appointed to succeed Duckett as the county's top prosecutor in 1988.

Other races that have generated interest include the District 30 House of Delegates seats. Two of the three seats are held by incumbents John C. Astle and Michael Busch, both Democrats seeking reelection. Republicans Phillip Bissett and former state senator Aris Allen are running, as are five other Democrats: M. Gerald Ackerman, Patricia Clagett, Barbara Neustadt, Edith Segree, Frances Baker, the first black woman to seek elective office in Anne Arundel, and Michael T. Brown.