Another high-volume year is foreseen for both new and resale housing but opinion differed here today on just how strong 1978 will be in terms of home buying.

"I see total new housing increasing from about 1.9 million in 1977 to 2.1 in 1978 with plenty of money available for mortgage loans on both new and resale houses," said John C. Opperman, a San Franciscan who is considerably more optimistic than others being made by housing leaders, in a panel discussion on the mortgage market held here during the 70th annual convention of the National Association of Realtors.

However, Harry Schwartz, Vice President and chief economist of the Federal National Mortgage Association, said he sees a "very slight softening" in the nation's housing markets and a slight trend upward in mortgage interest rates in the first half of 1978 that likely will hold housing starts to 1.7 million next year.

Schwartz' view was shared by Charles Pearce head of a savings bank in Quincy, Mass, and vice president of the National Association of Mutual Savings Banks. Pearce acknowledged a slight downturn in recent flows of new deposits into thrift institutions that make mortgage loans but he expressed confidence that disintermediation would not be serious because of the currently strong competitive position of those institution in vying for available funds. "An any federal income tax cut would reinforce that position," he added.