Plug-in hybrid electric vehicles (PHEVs) will be rolling out in force during the next 18 months, but the timing couldn’t be worse.

Back in 2007, PHEVs were rising from the obsession of fanatics who were doing their own conversion of hybrids to the planning playbooks of the major OEMs. At the time GM was making the most noise in hyping the Chevrolet Volt, and the company seems on target to make its end of 2010 deadline for producing the first vehicles.

But as I predicted it will be Toyota that will first bring PHEVs to market in the U.S., with the company promising to begin leasing vehicles here by the end of the year, 12 months ahead of GM. Toyota should rebound quickly as sales of its 3rd generation Prius are brisk, and that momentum should carry over to PHEV sales.

China’s BYD won the international race for PHEVs as the company started selling vehicles domestically and intends on selling into the U.S. next year. Other companies hoping to grow the PHEV market include Mitsubishi, Fisker Automotive, Chrysler, which has several models in the works, and Volvo, which will be the first to offer a diesel PHEV.

During the past two years, the environment for launching PHEVs has become much less inviting. The economic slowdown has forced Chrysler and GM into bankruptcy, and Ford is hanging on by a headlight. GM and Chrysler have leaned on the federal government for loans to retool for PHEVs, and GM is killing off a Saturn PHEV. Even Toyota, which blew away the competition to outsell everyone, experienced its first red ink in years.

Not only are the auto companies cash-strapped, but also so are many of the consumers who were expected to join waiting lists to buy the first PHEVs. The down economy has put hundreds of thousands out of work and significantly tightened credit, so the queues for PHEVs will likely be much shorter.

Another blow to the launch of PHEVs was last year’s crash in the price of gasoline, which is slowly creeping back up toward $3 in some states. Saving money by plugging in instead of fueling up was supposed to be one of the major arguments for buying PHEVs, but for now automakers will have to emphasize the environmental benefits.

Because of all of these financial factors, the introduction of PHEVs won’t be the instant revolution of autos that many had hoped for. In all likelihood, PHEV sales won’t take off in meaningful numbers until 2012-2013.

By that time, however, improvements in battery technology and economies of scale should slice about a quarter to a third from today’s hefty price premium, bringing PHEVs down to a more affordable level.