Apartment prices in Manhattan posted double-digit gains even as tight credit conditions and continued unrest on Wall Street slowed sales for the second straight quarter, according to two reports released Wednesday.

Real estate firm Prudential Douglas Elliman said the median sales price of a Manhattan apartment, including both condos and cooperatives, soared nearly 15 percent in the second quarter to $1.025 million _ or nearly the cost of five U.S. median-priced homes.

Nationwide, home prices dropped more than 15 percent in April from a year earlier, according to the most recent data from the Standard & Poor’s/Case-Shiller 20-city index.

In Manhattan, every type of apartment except three-bedrooms posted double-digit increases in median price, the Prudential Douglas Elliman report said.

But sales plummeted 22 percent as hesitant buyers wait out the unraveling of the financial markets and the uncertain job market or are sidelined by stricter credit standards.

Even so, sales volume remains significantly higher than the five-year quarterly average, said Jonathan Miller, president and chief executive of real estate appraisal and consulting firm Miller Samuel Inc., which analyzed the numbers for Prudential.

“There’s clearly a drop in sales activity in relationship to 2007’s unusually elevated levels, but in perspective, it’s still above what we’ve seen in the last five years,” Miller said.

A point of minor concern, however, is a sharp rise in the number of units on the market. Inventory ballooned more than 31 percent during the quarter, but still stands below historical averages.

“The macro view is we’re not seeing a bloated inventory, but inventory is clearly rising,” Miller said.

Apartments also are lingering on the sales block longer. The number of days on the market increased to 135 from 117 in last year’s second quarter. The five-year quarterly average is 126 days.

In a separate report Wednesday, real estate firm Brown Harris Stevens said sales volume in Manhattan dropped 18 percent from the April-June period last year. But like Prudential, the report showed a sharp jump in the median price.

“There’s clearly a softening, but not to the extent that a lot of people thought,” said James M. Gricar, director of sales for Brown Harris Stevens. “Revenue is staying roughly the same even though there were fewer transactions.”

Unlike the rest of the country, demand for Manhattan housing continues to outpace the supply on the market. The number of qualified homebuyers, especially for higher-priced apartments, is substantially higher in the city, Gricar said.

Most Manhattan cooperatives, which represent about 75 percent of the existing housing stock, have strict guidelines for financing. Many require a down payment of between 20 percent and 25 percent, but more upscale buildings require the buyer to pay all cash _ and those buyers have been scarcely affected by tighter lending standards.

“If the minimum down payment is 25 percent, then those buyers’ wherewithal is greater than those with a 5 or 10 percent down payment. It’s a self-selecting process,” Gricar said.

Prudential’s report is based on 3,081 home sales, while Brown Harris Stevens’ report tracked 2,988 sales.