What's the 811?

If you're planning a construction project and want to get the 411 on making sure you don't wind up having to call 911, soon the answer will be: Dial 811.

Between now and the spring of 2007, as a result of a new Federal Communications Commission order, Massachusetts and the other 49 states will begin phasing in 811 as a uniform, nationwide number for reaching ''Dig Safe" hotlines. The number 811 is the last of the available three-digit codes ending in -11 to be designated or deployed, following the well-known 411 for phone-number information and 911 for emergency help.

Laws in the Bay State and elsewhere typically require anyone doing excavation -- homeowners as well as businesses and institutions -- to call three business days in advance so utility workers can mark the locations of underground lines. The laws are intended to prevent the inconvenience or catastrophe that can result from striking an electric, gas, telecommunications, water, or sewer line.

Utilities in all the New England states except Connecticut already share a phone line, 1-888-DIG-SAFE. But around the rest of the country, more than 50 phone numbers cover various states or sections of states. Hoping to reduce the confusion, President Bush two years ago signed into law a pipeline-safety act that mandates the use of 811 nationwide -- once the FCC, utilities, and phone companies could agree on the details, which they did this month.

''Anything that makes it simpler and encourages people to call us to have these lines marked out, we're all for it," said Carmen Fields, a spokeswoman for KeySpan Energy Delivery New England, which serves over 800,000 natural gas customers in Eastern Massachusetts and New Hampshire.

Last year, Fields said, KeySpan responded to 286 incidents of damage to gas lines caused by construction workers who had failed to call for a Dig Safe inspection. Generally, however, the message has sunk in to ''call before you dig," Fields said. The 286 accidents contrasted with 150,000 completed calls over the course of the year for gas line mark-ups.

Lisa Faso, a spokeswoman for the New England Dig Safe agency, based in Woburn, said having a shorter, easier-to-remember number may marginally improve compliance with Dig Safe laws.

But, Faso said, officials are working out ways to resolve what happens when a contractor dials 811 from a border community in New York or Connecticut, seeking to have utility locations marked at a Massachusetts construction site.

Once 811 goes live, Faso said, the call would be routed to a Dig Safe center covering the state from which the phone call was being made, not the Woburn call center.

For that reason, Faso said, the center will continue using 888-DIG-SAFE indefinitely and will work with Connecticut and New York call centers to make sure they know when to alert callers that they need to call 888-DIG-SAFE.

Despite some small risks due to confusion or red tape, utilities generally say the benefits of 811 far outweigh any downside.

''We think it's overall a very beneficial solution that's good for the companies involved, and also good for the consumer," said Doug Sullivan, a director of federal regulatory policy and planning with Verizon Communications. ''Cable cuts cost Verizon a lot of money, and they can also be a serious inconvenience" for customers who lose phone and Internet access, he said.

Since the successful adoption of 411 for directory assistance and 911 for emergency police and fire service, several other three-digit combinations ending in -11 have been rolled out in recent years on a city-by-city or region-by-region basis.

The number 511, for example, is used in parts of Maine, Vermont, and New Hampshire for travel and traffic information. And 311, which the FCC has reserved for nonemergency municipal assistance, such as for garbage pick up or property tax questions, is being launched this year in Somerville and a handful of other city halls.

Peter J. Howe can be reached at howe@globe.com.