Henry Kissinger didn't show up at the Republican Party's platform committee hearings today, a media non-event that took on enormous proportion here, befitting the listless opening for preconvention week in Detroit.

Kissinger's nonappearance was actually a fleeting non-event. He will be here next week, when he is scheduled to speak to the full Republican convention in the evening, TV's prime time.

The flap over Kissinger's decision not to testify today grew out of published, and apparently erroneous, reports that he feared a hostile reception from the many extreme conservatives here.The distinctly conservative platform committee even gave a friendly welcome today to Michigan's unabashedly progressive Republican governor, William Milliken.

But there is no doubt about the ideological alignment on this GOP platform committee. When Kissinger speaks next Tuesday night, he is expected to echo the hard-line sentiments that are obviously ascendant here. If he takes any other course, Kissinger will find himself on a lonely limb.

But people who have been talking to Kissinger about his speech predicted that the former -- and, if his wishes are fulfilled, future -- secretary of state has no desire to be lonely in this gathering of Republicans.

The draft platform planks on foreign and defense policy that delegates began to consider today take a much harder line than Kissinger ever did in office in the Nixon and Ford administrations, which is why some delegates are unhappy at the thought of his appearance.

According to this draft platform -- prepared by the Republican National Committee staff and still subject to extensive revision -- a new Republican administration would all but abandon present U.S. foreign and defense policies, replacing them with new strategies that would cost taxpayers tens of billions of dollars in additions to the annual defense budget.

The draft platform was not officially released, but reporters had little trouble acquiring copies of it. The foreign policy section declares that "the United States faces the most serious challenge to its survival in the two centuries of its existence," and blames the Carter administration for most of the problems.

The current administration is "mired in incompetence" and has been "oblivious to the magnitude of the threat posed to our survival," the draft platform says. The administration's neglect . . . is without parallel since the 1930s."

The platform drafters appear to have shunned just one hard-line position: a return to a military draft. The "all-volunteer force has not been given a fair chance to succeed," the draft plank says, and it recommends expensive new pay scales, GI benefits and other measures to recruit and retain voluntary military personnel.

Other potentially costly recommendations in the draft platform include:

Accelerated development of the MX and Trident missile systems and of all cruise missile programs.

Development of a new manned bomber to succeed the B52 and substitute for the B1 canceled by the Carter administration.

Extensive new ship and plane-building programs to add vastly to the strength of the Navy and Air Force.

A new command and control structure for America's strategic forces.

The draft platform declares that "the Republican Party rejects the fundamentally flawed SALT II treaty negotiated by the Carter administration," and promises that a new Republican administrations only from a position of vastly increased American strength.

Preliminary discussions today among the 15 members of the subcommittee on foreign policy and defense revealed no inclination to back away from any of these proposed planks. On the contrary, there appeared to be strong sentiment for stiffening them.

Sen. Jesse Helms (R-N.C.), a member of the panel, told reporters he would be pressing for at least four toughened planks: one recommending the restoration of full diplomatic relations with Taiwan, one condemning any American aid to the new ruling junta in Nicaragua, one recommending protectionist trade measures to preserve on what Helms called the grave consequences on the Panama Canal treaties.

The foreign policy subcommittee's membership does not include any members of the traditional, internationalist wing of the Republican Party -- the wing once dominated by Nelson Rockefeller, under whose patronage Henry Kissinger first became a national figure.

Instead the committee is dominated by members of the Republican right. Its chairman is Rep. Jack Kemp (N.y.), a man hitherto better known for his interest in tax policy than in foreign affairs. The vice chairman is Faith Ryan Whittlesey, a conservative official in Delaware County, Pa. Helms, Sen. Roger Jepsen (Iowa), Kemp and Reps. Eldon Rudd (ariz.) and Floyd Spence (S.C.) are the only elected national figures on the panel.

Another member is former ambassador Earl Smith, U.S. envoy to Cuba in the last days of Fulgencio Batista's regime. Smith told a reporter today that his first objective was to write into the platform a plank calling for the revival of the Senate internal security subcommittee and the House Committee on Un-American Activities.