The widely heralded great debate on the Panama Canal treaty has already degenerated into a double snow job. The opponents started things with the kind of know-nothing argument regularly passed off as thought by Americans who are pleased to call themselves conservatives.

The administration was drawn to reply in kind. But the show biz staged at the White House around the treaty signing last week seemed to put off more senators than it pulled in.

Actually, the treaty raises several issues that merit extended debate. One issue is genuine doubt is moral. Has the United States, of all countries, the right to hold on to what is probably the most flagrant example of 19the century colonialism now extant in the world?

My own impression is that this country does not have a ghost of a case. But I would like to hear opponents of the treaty argue why this country should be vouchsafed advantages that allied nations such as France and Britain were obliged - largely under American pressure - to disgorge.

Another issue is practical. Does the treaty, as advertised, actually give the United States the right to intervene to protect the canal of its neutrality is threatened? My own impression is that Article 4 of the basic treaty absolutely guarantees this country's right to unilateral intervention. But I would like to see treaty opponents demonstrate from the text why American security is compromised.

In fact, the opponents want to talk about anything but the treaty itself. Former California Gov. Ronald Reagan not only testified against the agreement without having read the text, but he also boldly declared that it would be "a very grave mistake if we let ourselves be inveighed into debating what the treaties do or do no say."

Instead of debating the treaty, the conservatives want to talk about the fiber of modern America. Their tactic is to place the treaty in a long list of compromises with evils. They seek to make the backers of the accord defend all these supposed cave-ins.

A nice set of examples emerges from the mail being poured down on the Republican leader in the Senate, Howard Baker. A Memphis man wrote: "Why is it that a nation as strong as ours have [sic] had to give in so much since World War II? We have approached every issue on our hands and knees, from dealing with crime in the streets all the way to trying to be friends with the Communists."

A lady from Big Sandy, Tenn., asked Baker: "Are we chicken?" "When," a voter from Milan, Tenn., wanted to know, "is our government going to have the backbone to stand up to those two-bit, Soviet-controlled dictators?"

The Carter administration responded with a show of missionary real that has characterized its first initiatives on all foreign-policy issues, from arms control to human rights to withdrawal from Korea. The President staged a spectacular signing ceremony with Panamanian leader Omar Torrijos and representatives of all other hemispheric countries except Cuba. The White House also set in motion a parade of support for the treaty by such big names as former President Ford, former Secretary of State Henry Kissinger, the Joint Chiefs of Staff and all the stars of business and labor.

Apparently the idea was to isolate the conservatives by convincing the rest of the country and especially the business community that failure to ratify the treaty would bring trouble throughout Latin America. That effort was weakened because it took place before texts of the treaty were generally available. It actually embarrassed several senators who wanted to be seen making up their own minds - not being stampeded.

Thus only 23 out of 100 senators accepted the President's invitation to witness the signing ceremonies at the White House Wednesday night. One senator who was there noted that Torrijos gave a ceremonial embrace to both Carter and Ford. "The White House," he observed, "got the symbolism wrong. To show the [leader] of Panama happy with the treaty only confirmed the worst suspicions of a giveaway."

In the end the Senate probably will debate it on the merits. But the false start means that deliberations are going to take that much longer.

Majority Leader Robert Byrd is saying ratification annot occur this year. Perhaps that is a tactic designed to ease the immediate pressure. The probability is the debate will stretch well into 1978, thus complicating a host of other foreign-policy issues - notably arms control and the Mideast - that are truly pressing.