Credit unions, which enjoyed phenomenal growth a few years ago, can expect zero growth in savings during 1980, according to Robert Von der Ohe, chief enconomist for the Credit Union National Association.

He and the trade association's president James C. Barr, presented the gloomy outlook yesterday at a press briefing. They said the slowdown in savings inflows began in the second quarter of 1978 when other financial institutions began selling money market certificates, and peaked in October 1979 when credit unions experienced the greatest decline in savings ever, 2,64 percent, representing a $1.5 billion outflow.

As a result, Von der Ohe predicts the number of credit union liquidations will increase by 25 to 50 percent this year, while the number of mergers of weak credit unions into stronger ones is expected to rise by 50 or 100 percent.

One direct cause of the slump is a 45-year-old law limiting the interest rate ceiling on credit union loans to 12 percent. With market rates considerably higher, many credit unions have stopped lending altogether or have put $1,000 limits on loans. And because they are not earning money on loans, they cannot afford to offer high interest rate certificates to members.

Barr called the raising of the ceiling "our major legislative priority." Rep. Douglas Barnard (D-Ga.) has introduced a bill to raise it on a formula based on federal securities rates. At current rates that would allow credit unions to charge up to 15 percent.

Congressional banking leaders plan to consider the bill in March at the earliest after tackling the controversial issues of Regulation Q and Federal Reserve membership. "If they pass that (gradual lifting of interest rate ceilings) without the bernard amendment (raising credit union loan limits), we'd be out of business," Barr said.

Thus far the credit union industry has received no similar commitment from the Senate, but Barr called chances of passage excellent nevertheless. But Von der Ohe gives it little chance of passge if interest rates start to drop. There is a philosophical opposition in Congress and elsewhere to letting cooperative credit unions charge their mostly low and middle income members, high interest rates.

Even if the ceiling were raised, Von der Ohe said the action would come too late to help credit unions this year. A recession causing layoffs and strikes, which affect many members of industiral credit unions, can only worsen the situation.

In an effort to circumvent the 12 percent ceiling, Barr reports that substantial numbers of federal credit unions have applied for conversion to state charters. Some 30 states have usury laws permitting state-chartered credit unions to charge more than 12 percent interest on loans.

Other legislative goals include permanent legislation authorizing share draft accounts and tax incentives for savers.