Of South Florida’s three counties, Miami-Dade’s apartment sector is expected to fare better with vacancies in 2010 than its sister counties to the north.

Miami-Dade’s 6.8 percent vacancy rate placed it nearly at the middle of 44 apartment sectors ranked by their projected vacancy, according to Marcus & Millichap, the nation’s largest real estate investment services firm. The company ranked apartment sectors nationwide, using variables, such as projected vacancies and employment, to determine where each city fit in the big picture.

Miami-Dade’s vacancy rate ranked it 25th.

Peter Zalewski, of Condo Vultures Realty, says that the number of downtown Miami apartments still in the hands of developers has shrunk since 2008 to more than 7,000 from about 10,000.

Many buyers have introduced their new purchases into the rental market and developers who can’t sell their condos also are adding their inventory to the rental market. As a result, vacancies will grow and rents will decline, he said.

Jack McCabe, of McCabe Research & Consulting, said the downward pressure on rents is hurting older apartment buildings, particularly because there is so much new product out there at a discount.

In contrast, Broward County was expected to register a 9.3 percent vacancy rate, one of the highest in the country. Broward’s projected vacancy rate in 2010 actually pushed its ranking down five spots, to 39th from 44th last year.

Still, Marcus & Millichap expects the Broward market to stabilize in the coming year.

“In the investment arena, transaction volume steadied last year after several periods of steep declines,” said Gregory Matus, regional manager of Marcus & Millichap’s Fort Lauderdale office. “Sales of a few lender-owned properties boosted activity and additional financially distressed assets are expected to sell in the months ahead as rising vacancy, declining rents and increasing concessions place further pressure on cash flows.”

At No. 41, Palm Beach County recorded the worst ranking in South Florida because it was expected to have a vacancy rate of 9.6 percent by the end of this year.

Jacksonville fared the worst among all Florida cities, with an expected vacancy rate of 14.5 percent.

Looking at the raw numbers might be confusing because Washington, D.C., landed at No. 1, despite having a 6.5 percent vacancy rate. The rate is not that much better than Miami’s and higher than Los Angeles (6 percent), Milwaukee (5.5 percent) and New York City (3.4 percent).

Stacey Corso, spokeswoman for Marcus & Millichap, said Washington, D.C., had other things going for it that contributed to it top ranking, including strong prospects for job growth in the government sector.

Marcus & Millichap expects that Miami-Dade and Broward counties will see a job decline of less than half a percent. Miami-Dade is expected to see 3,000 jobs cut in 2010, an improvement from the 27,000 workers that were let go last year. Broward is projected to have 2,200 slots eliminated, compared with the 19,000 that exited last year. Palm Beach County is expected to have the least losses of all, with 2,000 jobs lost in 2010, compared with 15,000 shed last year.