The impression in Washington of fading political opposition to the Panama Canal treaties is refuted here by the experience of William Clements, Dallas oil-drilling millionaire and former Deputy Defense Secretary, in his surprise campaign for the Republican nomination for governor.

Clements started under a cloud for having backed President Ford's proposed canal treaty i 1976 while at the Pentagon. He changed to opposition against President Carter's version but still belittled the issue as not all that important. More experienced political advisers, shuddering in horror, soon switched him to an uneqivocal anti-treaty stance.

Nevertheless, Clement's semi-apostasy on the canla could cost him the nomination. It value is dubious anyway; polls and politicians heavily favor Demoncratic Gov. Dolph Briscoe for re-election. But the canal issue casts a long shadow forward to a 1980 struggle for possibly crucial presidential convention delegates from Texas.

The reality is the absence of any decline in opposition here to turning the canal over to Panama. That is partcularly true of the minority of Texans who vote in the Republican primary. So nobody supporting the treaties can hope for any Republican prize in Texas be it dubious honor of running for governor or the rich harvest of delegates to the 1980 national convention.

This political rule was not obvious to Clements when he surprised the tight little world of Texas Republican politics in November by announcing for governor at age 60, his first effort at elective office. That nomination had seemingly been nailed down by former State Rep. Ray Hutchiso, who until recently was Republican state organization support.

The argument being made for Clements by veteran paryt wheelhorse Peter O'Donnell and others is this: The governorship can be won only by a Republican who rounds up the "heavy hitters" - Texas big-money men - who habitually go Republican for President and Democratic for governor. With their clout, Clements might have a chance against Briscoe following a possibly damaging Demoncratic primary.

But given Hutchison's head start, Clements must win over the fervent, issue- oriented 1976 supporters of Ronald Reagan. They suspected Hutchison as state chairman was "neutral" for Ford against Reagan, and they mistrust Hutchison's close ties to former Gov. John B. Connally, who ended up backing Ford.

However, as ex-Deputy Defense Secretary, Clements too has Ford connections - including support for a Ford-sponsored canal treaty. it was not passive support. Texas newspaper editors can recall Clement's off-the-record pleas to support a treaty because the canal is militarity indefensible.

Although he opposes the Carter treaties, Clements tried to put the issue in perpective. Just before announcing his condidacy, Clements publicly declared the canal issue is far less important than strategic arms limitaiton talks. The treaty debate, he said, is "snapping at gnats." Even today, Bill Clements is condid enough to tell us: "If SALT is 10 on a scale of 10, then the canal is about 1."

Other Texas Republcan leaders feel the same way - but only privately - and Clements now has followed their lead by not volunteering his views to the grassroots faithful. On a recent visit to Midland in conservative west Texas, Clements declared himself, with no ifs, ands or buts, against giving away the canal. Mayor Ernest Angelo, an ardent Reaganite and Republican national committeeman, was satisfied.

However, Hutchison's backers point out their man has always been against the treaties without qualification. That may explain Clement's California pilgrimage the week before Christman to visit Reagan. He returned telling friends he was uthorized to say Reagan is "fully supportive of " his candidacy, but will make no announcement (a Reagan aide said Reagan was not asked for support but only advice.)

But Clements and Hutchison will both be deprived of Reaganite votes if Hank Grover, 1972 nominee for governor and a darling of the right, decide to run. Grover would be favored to be nomiated - and would guaranteee re-election of a Demoncratic governor.

More important is Panama's long shadow for Republicans eyeing the presidential race. having reaffirmed support for the treaties, Gerald Ford would have no more chance at winning the 1980 Texas delegation (to be selected through precinct caucuses) than he did in the 1976 primary slaughter. No other candidate can even hope for those delegates without opposing the treaties - a sobering reality for Republican presidential hopefuls undecided on the canal, notably Sen. Howard Baker (R-Tenn.). In Texas, at least, the Canal issue lives.