The largest public company in Los Angeles County remains oil giant Atlantic Richfield Co., posting $19.2 billion in revenues, and employing 22,700 worldwide. An integrated oil major, Arco has been the largest company on the List since the Business Journal started collecting data in 1986.

But Arco’s days as the top dog may be numbered.

Over the years, Burbank-based Walt Disney Co., under the stewardship of Chairman Michael Eisner, has grown steadily, and sometimes explosively, either by increased market share, new markets or acquisition.

In 1985, Arco posted revenues of $23.1 billion, compared with Disney’s $2 billion. Disney was then the 26th-largest public company in the county.

But times have changed. This year, Disney is the No. 2 company on the List, and with $18.7 billion in revenues, biting Arco’s heels.

By some measures, Disney eclipsed Arco long ago. On Wall Street, Disney had a market capitalization (shares outstanding times share price) of $50.1 billion as of this March 31; that was leagues above Arco’s market cap of $21.7 billion.

The market capitalization reflects the investment community’s much greater expectation of future profits from Disney than Arco. And indeed, no other company in the largest 20 companies has had near the growth of Disney in the last 10 years.

But there are other success stories.

El Segundo-based Computer Science Corp. was 43rd on the List in 1986, but this year it has moved up to No. 6 position. Revenues soared from $838.6 million to $5.6 billion in the same time frame.

Beverly Hills-based Hilton Hotels Corp., has jumped from No. 46 on the List 10 years ago to No. 10 now.

Another steady grower has been Pasadena-based Avery Dennison Corp., the label and office products manufacturer.

In 1985, Avery Dennison was the 39th-largest public company in Los Angeles County, with $932.7 million in revenues. On the List this year, Avery is the 15th-largest company, with $3.1 billion in revenues.

Some of the upward movement of companies on the List is due to attrition: Many of Los Angeles’ largest public companies have either been bought out, moved away or gone bankrupt.

Just some of the names on the List that have disappeared during the last 10 years: Lockheed Corp. (merged with Martin Marietta Corp. and moved away); Security Pacific Corp. (acquired by Wells Fargo & Co.); First Interstate Bancorp (acquired by BankAmerica Corp.); retailer Carter Hawley Hale Stores Inc. (acquired by Federated Department Stores); hospital chain National Medical Enterprises Inc. (bought out); retailer Wickes Cos. Inc. (went private); energy company Tosco Corp. (relocated); senior care chain Beverly Enterprises Inc. (relocated); Western Air Lines Inc. (taken over).

The make-up of the current 10 largest companies on the List reflects L.A.’s role as an entertainment, medical, energy, defense and high-tech capital.

Four of the companies, Unocal Corp., Occidental Petroleum Corp., Arco and Edison International are energy-related. Disney and Hilton are entertainment-related (Hilton through its extensive gambling properties). Northrop Grumman Corp. is defense, while Computer Sciences is high-tech. Wellpoint Health Networks, formerly a part of Blue Cross, is in the health care industry.

In comparison to last year’s List, there has been some minor jockeying.

For example, Computer Sciences moved to the No. 6 slot from the No 10 position last year, as revenues swelled to $5.6 billion from $4.7 billion. The computer industry remains a sector of high-growth companies.

And Hilton climbed to No. 10 this year from No. 22 last year, as acquisitions boosted revenues to $3.94 billion from $1.65 billion, (Hilton is now angling to buy ITT Corp.)

Another point about this year’s List: the relative size of the largest companies, in comparison to the local economy, appears to be diminishing.

The largest company, Arco, actually has smaller revenues than the List of 10 years ago, when it was also the largest public company.

Ten years ago, there were 33 public companies with revenues in excess of $1 billion; today there are only 29 such companies.

And the 100th company 10 years ago was Beverly Hills-based Wrather Inc., with $108.5 million in revenues. This year, the 100th company is Long Beach-based trailer maker KIT Manufacturing Co., with $97.2 million in revenues.

Corporate America has been in a major downsizing mode in the last 10 years, and that fact is reflected in local public companies, which have been trimming down.

As much commented, the Los Angeles economy today is a large sea of middle market companies, often privately held.