After 156 years of publication, the Church Herald of Grand Rapids, Mich., may soon be writing its own obituary. It survived the Great Depression, but the biweekly magazine of the Reformed Church in America won't survive another increase in postal rates.

In January, the cost of mailing one edition of the Church Herald to its 67,000 readers went up 110 percent, from $2,250 to $4,650. Now Congress has decided to raise it even higher, and the nation's religious publishers, along with thousands of other nonprofit organizations, are bracing for another round of sharply increased postal costs that is likely to put some out of existence.

The Church Herald is considered one of the nation's oldest religious periodicals, tracing its origins back to Henry Hudson and the Dutch Reformed Church. But the current editor, the Rev. John Stapert, said the publication probably will fold in October unless Congress scales back the increase.

The postal rate pinch is also squeezing many charitable and voluntary organizations that rely heavily on the mails for fund raising. The irony is that it will weaken the same groups that President Reagan is depending on to fill the gap left by his cuts in social programs.

For years, Congress set aside a subsidy that allowed nonprofit groups to mail in bulk at a reduced rate. The idea was that their newsletters, fund-raising appeals and publications served the public good, although critics had long contended the subsidy was unfair to taxpayers and other postal users.

In 1970, Congress approved a 16-year phase-out of the subsidy, but that schedule, which had six years left, has been abandoned.

Now, in the fervor to reduce large prospective deficits in the first budget resolution, Congress has ordered another slash in the subsidy, from $619 million this year to $400 million next year, in addition to the cuts made last year. This means another rate increase would come in October, raising the price of third-class bulk mail for a nonprofit group from 5.9 cents per piece to 7.9 cents. Mailing the same letter would have cost only 3.8 cents last January.

The nonprofit groups are now fighting back, lobbying the congressional appropriations committees to increase the subsidy. Rep. William D. Ford (D-Mich.), chairman of the House Post Office and Civil Service Committee, said the $400 million for next year is "so small and so inadequate as to be the equivalent of tossing a bone to a stray dog." (The subsidy was eliminated in the Republican budget resolution that first passed the House, but $400 million was restored in conference.)

More than just pennies are at stake for the March of Dimes Birth Defects Foundation, for example, which mails 120 million fund-raising appeals each year. The October rate hike will cost the group more than $1.5 million, said Clyde F. Shorey, a vice president. The March of Dimes sidestepped the January increase by mailing before the deadline, but that won't be possible this time, he added.

"What's happening is that Congress and the president are calling on nonprofits to help fill in the gap, and if they whack us with higher postal rates we're in a Catch-22 situation," he said. "We can't respond to it because we have to spend more money for mail."

Kay Hatch, director of the American Kidney Fund, told a House subcommittee recently that her organization, which relies heavily on direct-mail fund raising, has found a "direct and real" link between the increased postal rates and reduced financial aid for kidney patients.

Hatch said the fund now has 500 patients waiting for small amounts of financial aid--the average is $150 a month--but the forthcoming postal rate increase will cost the fund more than $20,000 a month.

A similar dilemma faces charitable groups because many states prohibit fund-raising solicitations if the cost to produce them goes above a certain limit. Hatch said the limit in Michigan, for example, is 30 cents for every dollar brought in. The kidney fund now spends about 27 cents. "With these postage increases, we obviously are going to be spending more money than they say we can spend," she said. "I can see that eventually being the demise of many organizations."

Stapert, editor of the Church Herald, acknowledged that religious, charitable and voluntary groups would have to accept higher postal costs in a time of lean federal budgets. But, he protested, "We can't allow the nation to put all of its culture on a profit-making bottom line."