It’s election season at the Los Angeles County Board of Supervisors, and once again what passes for a campaign is taking on surreal qualities.

Los Angeles County Supervisor Don Knabe has collected nearly $352,000 for his reelection bid from an array of contractors, builders, developers and casinos, even though no major challenger was on the horizon and he’s now running unopposed.

Two of Knabe’s colleagues have raised more than $800,000 between them. One has no challenger and the other faces a little-known Palmdale convenience store owner who has pledged to spend less than $1,000 on his campaign.

Amassing large campaign war chests for non-elections has become a tradition in Los Angeles County government.

An incumbent hasn’t been defeated in more than 30 years, and four of the five current supervisors have served at least 15 years.

Although Los Angeles City Council and other local races can draw a dozen candidates or more, analysts see the long dearth of competition at the Board of Supervisors as a vestige from a fading era of state and local government in which politicians could entrench themselves in a powerful post for a generation.

The five supervisors divide a county of nearly 10 million people, with sprawling districts that, individually, would each rank among the nation’s top 5 cities in population. Members represent districts with more people than 14 states, oversee the largest local government in the country and issue hundreds of millions of dollars in contracts each year.

The district of Michael D. Antonovich runs from Glendora to Lancaster, Knabe’s ranges from Marina del Rey to Diamond Bar.

The geographical sweep of their domains makes it difficult for local politicians to mount challenges.

Political experts said the big campaign funds that the supervisors often build up early, partly from those with financial interests in their decisions, serve as another deterrent. By collecting large sums before opponents emerge or when they face even token opposition, the supervisors can discourage potential challengers and the donors who might otherwise consider backing them.

In this reelection cycle, in addition to Knabe’s fundraising, Antonovich has collected nearly $364,000 with many contributions coming from developers in his district, along with engineers and contractors.Mark Ridley-Thomashas collected $444,000 with donations from numerous unions, healthcare workers and physicians, and attorneys.

“The amount of money you have to raise is almost insurmountable,” said Fernando Guerra, a professor of political science at Loyola Marymount University who also is a registered county lobbyist for an investment bank.

“When you merge incumbency with a very large district, the degree of difficulty becomes higher to the point where, barring any major crises or personal issues, it’s almost impossible to defeat” a sitting supervisor, he added.

Reelection funds that are not needed for actual campaigning can be used for anything “reasonably related to a political, legislative or governmental purpose,” according to state law. That gives the traditionally secure supervisors latitude to finance activities that can enhance their political operations and stature in the community, making them even harder to unseat in the future.

Knabe spent nearly $68,000 on consulting fees at a firm where his son is a partner, Englander, Knabe and Allen, according to documents. Harvey Englander was the supervisor’s campaign manager before Knabe’s son joined the firm, his spokeswoman said.

Antonovich’s reelection committee reported spending $4,000 for himself and two others to fly to an economic forum in China in September, a trip that was later publicized on the supervisor’s website, including a photo with the U.S. ambassador to China. He spent thousands more on gifts for staff members and constituents, including toiletries from Crabtree & Evelyn. (An Antonovich spokesman said the trip and toiletries were paid for from a non-campaign political account, but did not immediately explain why they were listed on reelection disclosure forms.)

Ridley-Thomas’ campaign committee reported spending more than $7,000 on a “Holiday Luncheon for Supervisor and 31 staff members.” Ridley-Thomas emphasized that the party actually included hundreds of staff members and constituents and he used campaign funds because he was prohibited from using another non-campaign political account in advance of the June election.

When no one ran against Gloria Molina in 2010, she stopped raising funds and spent about $100,000 to buy turquoise reusable totes for 90,000 households in her district. Molina has long championed restrictions on single-use plastic bags.

Contested elections or not, supervisors may feel a special need to raise funds and promote themselves because they tend to attract less media attention and voters often don’t understand what they do, experts say.

“What are you going to do when you get mad? You’re going to pick up the phone and call the mayor, even though maybe you should be calling the supervisor,” said William Fulton, a former Ventura mayor and senior fellow at the Sol Price School of Public Policy at USC.

The era of competition-free supervisorial campaigns may be headed for at least a temporary interruption. A decade ago, voters imposed 12-year term limits on board members. By 2016, four of the five current supervisors will be forced to step down.

“The clock is ticking,” said Sherry Bebitch Jeffe, a USC political scientist.

Indeed, the only highly competitive supervisorial race in recent memory occurred whenYvonne B. Burkestepped down in 2008, which sparked a fierce battle between Ridley-Thomas and Los Angeles City Councilman Bernard C. Parks. Unions spent $8.5 million in support of Ridley-Thomas, making the contest the most expensive in county history.

Some analysts expect that once a new crop of board members settles in, the pattern of comfortable incumbency is likely to return — until term limits force them out.

“It’s unlikely that when this massive turnover occurs that large political ... strife will” follow, Fulton said.

jason.song@latimes.com

ron.lin@latimes.com