In one bold move, a graying, 75-year-old economist-turned-politician transformed the face of Montgomery County's 1990 election season.

Neal Potter, veteran of the County Council for 20 years, strode into the county board of elections on Monday night, filed his candidacy for county executive and set up what promises to be a classic challenge with incumbent Democrat Sidney Kramer over growth and development.

The contest, pitting two of the county's better-known Democrats against each other in the Sept. 11 primary, tops the county's local races, but it is just one of the struggles Montgomery voters will decide this fall.

Montgomery voters also will decide an array of council races and will select four members of the county Board of Education.

The council races facing Montgomery voters are historic. Because of a change in the County Charter approved by voters in a 1986 referendum, Montgomery's council grows from seven to nine members, and, for the first time, five members will be elected from geographic districts.

The district elections, which are cheaper and easier to mount than at-large races, have attracted Republicans hoping to end the Democrats's 20-year rule of the County Council, as well as Democrats seeking to defeat incumbents they see as vulnerable in a year of citizen outcry over taxes and growth.

There will be primaries in all the districts except District 1, which includes the Bethesda and Chevy Chase area. There, Democrat Marilyn Goldwater, a former member of the House of Delegates, faces Republican Betty Ann Krahnke, a former member of the county Planning Board.

Democrats in the district number 39,961, compared with 24,294 for Republicans and 10,212 independents, but both candidates are well known and have been campaigning hard.

There are lively Democratic and Republican contests being fielded in District 2, which takes in the upper county, and District 4, the eastern portion of Montgomery.

District 2 is an open seat, with Del. Judith C. Toth facing real estate agent Vickie York in the Demoratic contest. On the Republican side, school board member Bruce A. Goldensohn faces civic activist Nancy Dacek.

District 2 is seen as one of the best opportunities for the GOP, with Republicans comprising nearly 39 percent of the voters. But Toth, considered by party observers to be a favorite over political newcomer York, has proven to be a top vote-getter in the district. York is running on the incumbent slate of Kramer.

In District 4, incumbent Democrat Michael L. Gudis faces a stiff challenge from school board member Marilyn J. Praisner. Praisner has lined up several officials in her camp, such as Potter and Planning Board member Carol Henry, but Gudis is better-financed. The candidates already have sparred over growth and campaign spending.

On the Republican side, former school board member Carol F. Wallace is facing GOP activist Robert L. Clark Jr.

In District 3, which includes the Rockville area, Council President William E. Hanna Jr. faces an admittedly uphill challenge from political activist Anne Robbins in the Democratic contest. Stephen Abrams, a former Rockville City Council member, will run as an independent. Abrams, a federal employee, switched his party affliation from Republican because of Hatch Act prohibitions.

District 5, the heavily Democratic area of Silver Spring and Takoma Park, has a crowded field of Democrats vying for a seat left open by incumbent Rose Crenca's decision to run countywide.

Takoma Park City Council member Marc Elrich, who has been a tough critic of county plans for the redevelopment of downtown Silver Spring, became the latest candidate to enter the fray, filing his candidacy Monday night. Other candidates are Dianne Smith, a PTA activist running on the Kramer ticket, lawyer Derick P. Berlage, and civic activists Susan Heltemes and Elizabeth "Betsy" Taylor. The winner of that contest will face Joan Ashley Ennis, a civic activst who aborted her Democratic candidacy in a switch to the GOP.

Primaries will be held in both parties for the four at-large council seats. Seven Democrats have entered the race, including the four incumbents -- Crenca, Bruce T. Adams, Isiah Leggett and Michael L. Subin.

Seeking to defeat an incumbent Sept. 11 are Gail Ewing, a former council aide, Silver Spring civic activist Gene Lynch and county bus driver Michael A. Cafarelli Sr.

County Republican Chairman Richard LaSota, a county schoolteacher, decided to back up his call for an end to one-party rule with his own candidacy. LaSota enters the GOP at-large primary against architect John F. Thomas, lawyer Robin Ficker, civic activist George Edward Sauer and Edward R. Shannon, who could not be reached for further information.

Meanwhile, the four school board races will produce an unusual number of new members on the seven-person body that oversees Montgomery's 102,000-student school system. Praisner and Goldensohn are relinquishing their seats as they run for the council, and the board's president, Robert E. Shoenberg is retiring.

The elections also have the potential to bring more ethnic diversity to the board, whose current members all are white. This year's field includes a black candidate and, for the first time, an Asian American candidate and another who is Hispanic.

In the legislative races, Steve Silberfarb, who launched the first challenge of state Sen. Margaret C. Schweinhaut (D-Montgomery), said he was getting out of the race for the same reason he got in -- the abortion issue.

Silberfarb, announcing Monday that he would run instead for House of Delegates in District 18, said that he couldn't run the risk of splitting the abortion-rights vote with Del. Patricia R. Sher (D-Montgomery). Sher and Silberfarb are advocates for abortion rights, while Schweinhuat is staunchly anti-abortion. Two abortion-rights candidates, Silberfarb said, could mean election of someone anti-abortion. Silberfarb said he wouldn't be able to look himself in the mirror if that happened.

Schweinhaut, meanwhile, joined with Del. C. Lawrence Wiser (D-Montgomery) to announce they were running for reelection on a slate filled out by political newcomers Robert Abrams and Richard Davis. Wiser, Abrams and Davis said they are all abortion-rights advocates, but that they didn't believe in single issue elections.Staff writer Amy Goldstein contributed to this report.