The Post's assertion that the so-called ''evangelical right may be losing its political punch for 1988" because of the recent episodes involving Jim and Tammy Bakker and Oral Roberts could not be further from the truth {news story, July 19}. The reason, of course, is that neither Jim and Tammy Bakker nor Oral Roberts represents the entire religious right. Also, neither of these televangelists has been very active politically.

In fact, the conservative Christian movement is poised to exert its strongest political influence ever. During this decade, people such as Jerry Falwell and Pat Robertson served a valuable public role by focusing Christian attention on issues and encouraging political participation. During the same period, thousands of ministers around the country joined them in urging their flocks to get involved in politics.

A decade ago these same ministers had preached that politics was a dirty business and that their parishioners should concentrate on personal piety and evangelism. We have gradually seen a remarkable reversal in this attitude. Falwell, Robertson and such organizations as Christian Voice began exhorting Christians to get involved in politics in order to change a society that had legalized the taking of innocent unborn life, that prevented children from praying in school and that allowed pornographers to thrive virtually unchecked. The support of these religiously motivated voters helped ensure that Ronald Reagan was twice elected president, and Jimmy Carter once.

The ''religious right'' is now entering a new decade and adopting new tactics that should make its effectiveness even more pronounced. Although these groups have in the past operated largely autonomously and independently, the frustration of unrealized expectations during the Reagan years, coupled with a growing realization of the enormous power inherent in these groups if they act in concert, is resulting in historic new coalitions. Their efforts are breaking new ground as they cut across racial, ethnic and party lines to unite around the moral issues.

This bodes well for candidates for public office who support traditional values. Backing for those candidates will be amply available.

The conservative Christian community is not disillusioned nor is it going to dry up and blow away. It is perhaps bruised by the antics of the few, but at the same time possessed of a sense of resolve to be a dominant voice in national affairs. -- Robert Grant The writer is chairman of Christian Voice.