Home sales in the San Francisco Bay area plummeted to a three-year low in April, dampening optimistic reports from a month earlier when area homeowners sold 7,051 homes, research firm DataQuick said Monday. The La Jolla, Calif.-based  firm says 6,789 residences were sold in the nine-county Bay Area last month, a 3.7% drop from March and down 3.1% from a year ago. Bay Area home sales in April hit their lowest level in three years and became the third-lowest record to date, DataQuick said. April sales over the course of the past 16 years have been as low as 5,636 in 1995 and as high as 14,430 sales in 2004. The average April sales figure is roughly 9,147 homes. The total sold last month fell 25.8% below the average benchmark. “April activity looks weak on the heels of March, which eked out the highest sales for that month in four years,” said John Walsh, DataQuick’s president. “But it’s also to be expected that sales and other statistics will behave more erratically these days.” The median price on all resale and new homes in the Bay Area in April was $360,000, which is flat with March but down 2.7% from $370,000 a year earlier. Write to: Kerri Panchuk.