Office rents in Midtown, the highest in the nation, may rise 10% to $55 a square foot by the end of 2005, reversing a four-year trend, according to CB Richard Ellis Group, the world’s largest commercial real estate brokerage.

Available space in Midtown, the commercial center of the city, could fall to about 9% by year’s end, from 10.6% today, said CB’s New York Tri-State co-chairman, John Powers, in the company’s annual forecast. Vacancies had tripled to 14% between 2000 and 2003, according to company data.

The rent increase signals that Manhattan, the largest American market for office space, has regained its stature as a corporate center, Mr. Powers said. The boost could shift growth to Lower Manhattan, depressed by the 2001 World Trade Center attacks, where the vacancy rate is 16.6%, the company said.

“Pricing pressure will be heavily felt by the few tenants searching for blocks over 250,000 square feet, with only four such blocks readily available,” Mr. Powers said. “Prices have increased and will continue to do so along Park Avenue and Times Square West.”

More Midtown office leases were signed in 2004 than any year since 1997, he said, led by Bank of America’s 1.1 million square feet at the One Bryant Park office tower and PriceWaterhouseCoopers’s 789,000 square feet at 300 Madison Ave.

About 18 million square feet was leased for offices in 2004, almost twice as much as 2002, the company said. Midtown Manhattan, mostly between 34th and 59th streets, has 331 buildings and 196 million square feet of office space.

Rents in Midtown peaked at $62 a foot in 2000, then fell as financial service firms like JPMorgan Chase & Co. and Morgan Stanley fired workers and pulled back on expansion plans. Rents stabilized around $50 a foot in 2003.