Ending a four-year labor battle, the largest property owner in downtown Los Angeles agreed Tuesday to create a union local for private security guards - a move that officials hope will lead to unionizing efforts in other privately owned buildings.

Rob Maguire of Maguire Partners, which owns the seven biggest buildings in downtown Los Angeles, announced the agreement with Mayor Antonio Villaraigosa and union officials at a City Hall news conference. The plan affects more than 300 security guards employed at Maguire's buildings.

"This is a historic moment in the effort to bring fair wages to these workers," Villaraigosa said. "What's important is that it is Rob Maguire who is doing this and it sends a message to other building owners to sign on."

Maguire long has been a key figure in persuading private business owners to accept union contracts. He was the first to negotiate with Justice for Janitors, ending a weeks-long work action several years ago.

"I have always believed in paying fair wages and providing health benefits to workers," Maguire said. "I think we get better productivity and a lower turnover. I just needed some assurances here."

Key to the agreement - which Villaraigosa said he believed would serve as a template for other building owners - is creation of a separate local within the Service Employees International Union.

The SEIU is one of the nation's fastest-growing unions, representing a broad cross section of government and private industry workers. Its Local 347 is one of the largest in L.A. city government, representing some 10,000 of its lowest-paid employees, including clerks, sanitation workers and janitorial staffers.

"For reasons of security and to make sure we could operate our buildings, I did not want to have the security guards represented by the same union that represents our janitorial staff," Maguire said. "Once we got that resolved, the rest was easy."

The proposal - with wages still to be negotiated - also includes $750,000 for additional training for security officers to be paid by Maguire and the SEIU over the next three years.

Villaraigosa said he considered the fund a key element because of the need to deal with homeland security.

"I have become convinced that these private security guards are important first responders in the event of an incident and we need to professionalize their work force," the mayor said.

He indicated he has been talking with other property owners and expects them to also soon reach agreement with the SEIU. Villaraigosa said he believes the union will grow to become one of the largest in the city, with some 10,000 members.

Jono Shaffer of the SEIU said the agreement sends a message to other building owners that the union will be there in the future.

"We are not going to back down," Shaffer said. "This says to all the other building owners that this movement is real."

The agreement comes as several other city officials have announced plans for hearings into the security guard industry as it relates to training and pay.

Business groups have come out against that proposal, saying the issues should be dealt with through negotiations.