Upon Bob Beall's arrival in Pittsburgh a few years ago, he took the advice of a national yellow pages agency and bought space in Verizon's Allegheny County phone book for his Mr. Rooter plumbing franchise.

If only it were still so simple. These days, Beall's business has ads in the Verizon book, the Yellow Book and smaller directories such as the North Pittsburgh Telephone Co. version. The plumbing franchise has even begun advertising in online directories.

The $14 billion yellow pages industry, once a rather sedate Ma Bell monopoly, has undergone a competitive explosion. The Yellow Pages Association estimates more than 7,000 traditional U.S. directories offer listings, with a new one published almost every day of the year.

Just which of the often hefty publications is being picked up when people need a plumber is not always clear.

Faced with the threat of losing national ad dollars to other mediums, the industry has wrestled its sometimes bickering members into tackling a problem that threatens all of them: the lack of a respected, third-party referee. It is hoped that telephone surveys that begin this month in more than 90 markets from Pittsburgh to Los Angeles to Milwaukee will give the yellow pages what TV has with its Nielsens and radio with its Arbitron ratings.

"We need to give our clients some answers," said Stuart McKelvey, president of TMP Worldwide Directional Marketing, which claims to be the world's largest yellow pages advertising agency, handling placements for companies such as Pizza Hut and Ford Motor Co.

Clients have begun insisting on answers. In July 2002, two key groups -- the Association of National Advertisers and the American Association of Advertising Agencies -- paired up for a position paper noting that total yellow pages ad spending was just slightly behind that on the primary four TV networks.

National advertisers as a group spend $2 billion on yellow pages spots, and a large company flies its banner -- and its telephone number -- in as many as 300 to 600 books. "It is unthinkable that investment decisions for television and magazines would ever be made without the benefit of audience research. Why should the yellow page advertising medium be any different?" the groups' position paper said.

Plenty of research is actually done on the industry. Firms already rate which categories are most effective. People pull out the books for emergency repair services such as plumbing and automotive calls but may choose the Internet for travel services or auto dealers. Individual advertisers also sometimes put special numbers in ads so they can tell where callers saw the spot.

In the late 1990s, there was even directory use research. But it did not hit all major markets regularly and, as competition grew, the debate on how to get everyone from regional Bell companies to independent directory publishers to help foot the bill didn't reach a consensus in time to keep it going.

Some publishers did not seem eager to have ratings anyway, a concern that frustrated agencies placing ads. "Imagine if the TV folks said, 'We don't like the answers, so we're not going to pay,'" said McKelvey.

The implied threat from national advertisers in 2002 got the parties back to the table.

Blanche McGuire, a senior vice president at Ketchum Directory Advertising's Pittsburgh office, co-chaired the committee that worked out a format that would meet the need for unbiased research.

Like TMP Worldwide, Ketchum helps national advertisers identify the best books for them and coordinates the myriad deadlines. "Ketchum has been fighting for this kind of measurement for more than 20 years," said McGuire. Clients have more options for their marketing dollars now, creating pressure to prove a return on the yellow pages investment.

TMP Worldwide was bothered enough by the lack of information that it developed its own directory assessment tool in fall 2003, an estimate based on barometers such as the size of the market, how long the directory had been published and whether the page count was going up or down. McKelvey, the agency's president, expects that the new research will bring the credibility of an impartial outsider.

Now that 15 yellow page publishers have signed on to the project, everybody is waiting with some uncertainty to see what the researchers find. Results from the telephone surveys and subsequent analyses won't be available until 2006.

The hope is directories prove worth every penny spent on them. The dream is they can make the case for more.

"We'd love to see it lead to increased spending," said Nancy Augustine, vice president of the Association of Directory Marketing, a Moon-based group that represents yellow page agencies.

At Mr. Rooter of Warrendale, which is in Cranberry, Bob Beall expects online phone services to keep growing and predicts the books will eventually be turned into discs dropped off for use on the kitchen computer. By some estimates, some 60 percent of people who have regularly used the Internet five years or longer use Web yellow pages.

Still, Internet yellow page revenues make up just a fraction of overall industry spending -- about $300 million of the $14 billion total, said Larry Small, research director of the Yellow Pages Association.

For the moment, Beall is a yellow pages believer. Using research provided by TMP Worldwide, he has bought a prime position on the spine of both Verizon and Yellow Book directories in Allegheny County for a few years and plans to continue.

Verizon brings in more phone calls but also costs more than Yellow Book, so Beall figures dollar-for-dollar he may be getting more value from the latter, newer book. That reasoning could make the new research valuable even for directories that do not dominate, said Mc-Kelvey.

Beall sees the yellow pages as a reliable way to get his company's name in front of people with a clogged drain. Yet for a big, short-term pop, he periodically buys space on 30 or so roadside billboards. "My calls double."