Calling transportation a vital issue for business and anyone who lives or drives in San Diego County, two groups are hosting a public forum on Proposition A, a measure to extend a half-cent sales tax to pay for transportation improvements

Organizers said the forum is meant to provide information on the measure and give the public a chance to ask questions about the tax extension, which would raise $14 billion for improvements to freeways, surface streets and public transportation.

The forum is scheduled for Thursday in Lake San Marcos. The 90-minute forum, which starts at 8 a.m., is being put on by the San Diego North Economic Council and the North County Chambers Association, local business groups.

Representatives of the San Diego Association of Governments, the region's transportation agency, will give a presentation on TransNet, the tax that would be extended under Prop. A. While employees of the association, it can't advocate for the measure because they are public employees, they can provide information about the proposition.

The audience will then get a chance to ask questions, said Gary Knight, the interim president and chief executive of the economic council.

"We're trying to keep it away from being a debate," Knight said. "It has to be informational."

Prop. A would extend TransNet for 40 years beginning in 2008. The tax was first approved by voters in 1987 and first levied on April 1, 1988.

If passed, revenues from the extension of the tax will be split roughly into thirds among freeway projects, surface street improvements and public transportation.

The measure's critics, including three of five county supervisors, say more money should go to freeways, which carry the bulk of commuters. Supervisors Bill Horn, Dianne Jacob and Pam Slater-Price and North County's Republican legislators have said the plan should give 50 percent of revenues to highways.

A number of environmentalists, on the other hand, have said too little is planned for public transportation.

Under the plan, money would be dedicated to improving Interstates 5, 8, 15 and 805, Highway 78 and state Routes 52, 54, 56, 67, 76, 94 and 125. Surface streets and commuter rail and bus services would also benefit.

"It's an important issue countywide," said Joe Gabaldon, the chairman of the board for the council. "TransNet money has provided improvements throughout the county. There are issues to consider if we're going to renew this again."

The Lake San Marcos Resort is at 1025 La Bonita Drive, from Highway 78 take Rancho Santa Fe Road south to Lake San Marcos Drive follow the signs to the hotel.

To RSVP for the forum, which costs $10 and includes a continental breakfast, call the San Diego North Economic Council at (760) 598-9311. Registration will start at 7:30 a.m.

Contact staff writer Katherine Marks at (760) 740-3529 or kmarks@nctimes.com.