A new escalation for Rep. Jack Kemp was reached here Aug. 24 just before the Buffalo, N.Y., congressman's speech to a fund-raising dinner when he talked to wealthy South Carolina textile magnate Roger Milliken.

Kemp and Miliken conferred in whispered tones at a cocktail party for big contributors before the dinner. Kemp revealed to Milliken what he had not made public: He is about to create a PAC (Political Action Committee) authorized under law to collect contributions. Milliken quickly volunteered that he wanted to be among the first to contribute.

No bridges were burned on either side. By setting up a PAC, Kemp does not commit himself to running for president or any other office. By contributing to Kemp's PAC, Milliken does not commit himself to a Kemp presidential campaign. Nevertheless, there are the seeds of commitment from each of them.

Kemp's PAC (to be run by broadcasting executive Frank Shakespeare) presumably will bring order to the congressman's coast-to-coast meanderings - without speechwriter, advance man, research aide or even coat holder. Although the PAC's ostensible purpose is to boost Kemp's tax-reduction crusade, it is the essential first step toward seeking the Republican presidential nomination in 1980.

Milliken, long a quiet but bountiful contributor to conservative campaigns, was a major giver to Ronald Reagan in 1976. But he privately questions whether Reagan ought to run in 1980 at age 69. So Milliken is looking closely at Kemp, soem 25 years Reagan's junior, as the alternative.

This was the pattern of two hectic days' campaigning by Kemp Aug. 24 and 25, while Reagan and Rep. Philip Crane (the first announced presidential hopeful) were vacationing. Despite Kemp's shortcomings in both technique and substance, there were twin surprises of volunteered presidential support for Kemp and lack of enthousiasm for Reagan. It is significant because Kemp, after starting the swing in Cincinnati, moved into Reagan country: South Carolina and Mississippi.

This is the Kemp phenomenon. While senior Republican collegues in the House consider the former football quarterback as much too pushy, Kemp is the instant hero on the Republican banquet circuit by virtue of his tax-cut gospel. He need not, as Jimmy Carter was still doing in 1975, explain who he is; no stop was free from spontaneous urgings for a Kemp presidential campaign.

Kemp's charisma coexists with confusion. Without an aide to push him along, Kemp missed commercial flight connections from South Carolina to Mississippi. He flew into each stop oblivious of local situations and many local leaders.

A potentially more serious problem is obsessive stress on tax reduction as the philosopher's stone to save Western civilization. During two days, Kemp carried on a non-stop economic seminar on tax reduction - in speeches, press conferences, meetings with politicians, and in just plain bull sessions. Sooner or later, he must broaden his message.

Yet Kemp's monomania enables him to skirt social issues so pleasurable to hard-core Republicans but of dubious political value-busing, abortion, crime, homosexuality, drugs. Furthermore, Kemp rejects demands by Republicans that his tax reduction to restore incentive be balanced by deep spending cuts.

"I believe we ultimately will need to spend more money," he told a Cincinnati press conference, for national defense and "to clean up air and water."

In Columbia. S.C., while shocked Republicans gaped over breakfast, he committed heresy: declaring that "the cause of inflation is not unions"; praising John F. Kennedy's tax cuts and criticizing Herbert Hoover's tax increases; attacking the "meat ax" $100 billion federal-spending cut of Howard Jarvis and preferring something "more humane, more compassionate, more positive."

At that South Carolina breakfast, Kemp was preaching specifically to Gov. James Edwards, trying to convince him a balanced budget is not the first priority. Edwards is definitely interested. A Reagan stalwart in 1976, he still feels a strong pull to follow him. Yet, like Milliken, Edwards wonders whether a last hurrah is in the best interests of either Ronald Reagan or the Republican Party.

But why don't Edwards and Milliken opt for the more conventionally conservative Phil Crane instead of Kemp? That goes to the heart of the Kemp phenomenon. "He leaves the audiences with hope, not anger," explained one party leader after listening to Kemp. That is so unusual a feat for a Republican that it explains why he has surmounted inexperience, confusion and a narrow-based idea to become, for now at least, a welcome excitement in an habitually drab political party.