Fairfax County’s plans for redevelopment in Tysons Corner are giving at least one developer pause.

Real estate developer AvalonBay has junked designs for two new apartment buildings in the Northern Virginia suburb, citing the potential cost of public improvements — a setback for an area where officials would like to see 80,000 people relocate by 2050.

Based in Arlington, AvalonBay is one of a slew of real estate investment trusts, or REITs, which have begun developing and renovating apartment buildings in the Washington area to take advantage of low vacancy rates and construction costs. There are 12 apartment buildings being built by REITs slated to open in the next 24 to 36 months throughout the region.

In Tysons, AvalonBay had planned to build apartments on Tyco Road, about one-quarter of a mile from the Tysons West Metro station, which is scheduled to open in late 2013. The company bought the 5.5-acre site in 2005 and had planned to tear down the existing warehouses there last year to make way for two six-story apartment buildings.

But Jonathan B. Cox, senior vice president for development at AvalonBay, said the company has put the plans on hold indefinitely. At issue, he said, are $810 million in road improvements included in the plan Fairfax County adopted last year.

“It’s just that the new comprehensive plan — I don’t feel good about it. It’s outrageously expensive what they’re asking to be done,” Cox said.

County officials argue that private sector investment is needed to finance the rest of the $810 million price tag. They have discussed funding the road improvements but have not made a decision. The Georgelas Group recently won approval to build five apartment buildings near the AvalonBay property, after the company agreed to pay for some road improvements.

But Cox said the uncertainty meant he could not estimate what the apartments would cost to build. He said he didn’t want to be “sitting around the next couple of years and spending a few hundred thousand dollars on plans” without knowing the costs would be reasonable.

The company still is building in Tysons Corner; it plans to open 354 units in its Avalon Park Crest development in the summer of 2012. But in Tysons West, it plans to rehab its existing warehouses, which are now likely to greet Metro’s first riders as they disembark.