An upturn for local advertising agencies and PR firms is another piece of evidence that the recovery is under way.

Total billings for the 20 largest ad agencies in Los Angeles were $3.6 billion last year, up 8 percent, based on data on the Business Journal’s annual list. In the smaller public relations sector, billings at the top 20 agencies reached $78 million, a 4 percent increase.

Eric Johnson, co-president of Santa Monica-based advertising trade group thinkLA, said that after two years of budget cuts, advertisers switched to spending mode last year. A raft of product launches helped buoy the numbers.

“There’s now an enthusiasm in the market and we’re seeing fairly robust growth for accounts locally, regionally and nationally,” Johnson said. “That bodes well for the economy as a whole in 2011 because advertising is often seen as a leading indicator in a recovery.”

Johnson, who is also president of Ignited, an El Segundo ad agency not on the directory, said that TV spending has increased significantly. A trend, though, is that advertisers steered away from the major networks and invested more in cable channels. The other major growth occurred in digital, while print and radio continued to decline.

Broadcast accounted for 43 percent of total billings on the advertising list, while the Internet represented 25 percent.

In the PR sector, digital also led the growth as agencies added social networking and interactive websites to their list of services.

Rachel McAllister, co-chief executive at mPRm Public Relations, the number eight agency on the directory, said clients are optimistic about the prospects for increasing sales in 2011. They are asking their PR agencies to include a social media strategy in addition to traditional outreach methods such as events and news releases.

“Historically, PR was going through media outlets to reach audiences,” she said. “Now there are means to go directly to the audience and the opportunities to touch the audience directly are going up exponentially.”

Johnson said the advent of social media has blurred the line between PR and advertising, a trend he expects to continue in 2011.

“Ten years ago, PR agencies wrote press releases and organized junkets, but now they handle reputation management, social media and blogger relations,” he said. “More and more, they are moving into what might be called digital marketing.”