According to Standard & Poor’s/Case-Shiller 10-City Composite Index released on Tuesday, home prices plunged by a record amount nationwide in September, but California’s price decline in October was less than the record drop posted the previous month.

The recorded 16.6% decline in the third quarter, compared with the same period last year, eclipsed the previous record of 15.1% set during the second quarter. Prices in Case-Shiller’s separate index of 10 major cities fell a record 18.6%, while its 20-city index dropped a record 17.4%.

These indexes are released on the last Tuesday of each month, and they track sales and resales of individual houses, wherein the losses or gains correspond to actual price changes. With foreclosures soaring at record rates, the economic picture dimming and job losses ramping up, all the elements were in place to push prices lower.

Since May, Case-Shiller’s national monthly declines have rested around 1 percent, with observers speculating that the markets were approaching a bottom, months back. In Tuesday’s report, the declines were 1.9 percent for the 10-city index, and 1.8 percent for the 20-city index. The change is not large and could in part reflect seasonal home-buying patterns, which typically slow down at the end of summer.

Susan Wachter, professor of real estate at the University of Pennsylvania’s Wharton School of Business, said: “The key point is we do not yet see a deceleration. This is another historic decline and the drivers are still pointing down.”

Standard & Poor’s expects it will take at least until the middle of next year before the housing market bottoms outs and until 2010 before prices begin to climb.