Having mothered a budget agreement that even he cannot love, James A. Baker III returns from Thanksgiving in Texas on the razor's edge, with trade and dollar decisions that will shape the future more than his deficit-reduction fix.

To call the secretary of the Treasury overburdened is an understatement. He is the administration's uncrowned economic czar, wielding power over budget, trade and currency. Nobody effectively challenges him from within. Yet on testimony of even friendly onlookers, he is dangerously short of skilled advisers.

In this condition, Baker faces three exacting decisions: first, how to fill in the $9 billion blank check for taxes without crippling the economy; second, to determine whether confrontation is better than conciliation with congressional protectionists; third, to plot strategy for the seven big industrial democracies (G-7) in stabilizing currencies.

Based on Baker's budget performance, confidence is not high. As he left for Texas last Wednesday, a letter went to President Reagan on why the budget settlement did not energize financial markets. ''I will tell you,'' wrote Paul Craig Roberts, an architect of Reaganomics as assistant secretary of the Treasury in 1981-82, ''because no one who works for you will.''

Pioneer supply-sider Roberts told the president ''you gave up a strong position based by the automatic Gramm-Rudman sequester {of spending} for a weak one'' enabling Democrats to avoid domestic spending cuts. ''Your aides could not resist the temptation to sell out your policy in exchange for media stories portraying themselves as flexible pragmatists who know how to work with Congress and get things done. It is the easiest thing in the world to work with Congress. All you have to do is to give in.''

The need to ''work with Congress'' was stressed by Baker when he returned from Europe Oct. 20, the day after the crash. After persuading the president to backtrack on anti-tax-increase pledges, he told Reagan repeatedly during the talks that reversion to Gramm-Rudman cuts would be disastrous for markets at home and abroad.

With the same mindset, Baker rejected advice that the president demand Congress set aside trade legislation. Desire for compromise also is suggested by the administration's newly bellicose stand on trade. Baker's message to Congress: We're going to be tough, so please don't give us a bill we can't sign.

Imposing trade sanctions against beleaguered Brazil was followed by an unexpected onslaught against Asia's ''Four Tigers'' -- South Korea, Taiwan, Hong Kong and Singapore. The outside world was stunned Nov. 17 when Assistant Treasury Secretary David Mulford attacked them for not increasing the value of their currencies to the detriment of U.S. trade. But trade insiders knew that two weeks earlier Baker had ordered punishment of the Four Tigers by ''graduating'' them from special status, depriving them of duty-free access to the U.S. market.

This incident built concern on Capitol Hill that Baker's burden is too heavy. The secretary is described as walking into a Cabinet-level meeting ''in a fit of pique'' and, frustrated by Asian obstinacy, ordering punishment -- without prior interagency staff review. Only later did the bureaucrats report that what Baker wanted was impossible under the law.

That confirms congressional complaints that the usually well-prepared Baker is flying blind on trade because of insufficient preparation. That may also explain Baker's comments, again when preoccupied by the budget talks, which were interpreted as talking down the dollar. Federal Reserve Board governors were stunned at the normally punctilious Baker publicly attacking their discount-rate hike. Baker triggered a free fall in the dollar that was not arrested until the president himself reassured markets.

One problem is that Baker has failed to find another idea man to replace the departed Richard G. Darman as deputy secretary. Since Darman left April 13, the United States has proposed no new currency initiatives. Last February's Louvre agreement, intended as an eight-week expedient setting target zones for exchange rates, failed as a permanent settlement.

But Baker meets opportunity at the next G-7 meeting, probably in Paris before year's end. There are signs that the G-7 finance ministries' obsession with the U.S. budget deficit is being replaced by interest in the American economy's buoyancy, as expressed in 4.6 percent growth last quarter. Aware the appreciating deutschemark is savaging conservative farmers in their party's deteriorating northern base, West Germany's Christian Democrats may be ready to stimulate their own economy and stabilize exchange rates.

In a tired administration where caution rules, Jim Baker remains a superb inside operator. But without an ideological agenda, what course will he now follow? The course of least resistance on Capitol Hill leads to heavier taxes, trade restrictions and a falling dollar. With a Craig Roberts no longer around to sound alarms and no Dick Darman to float ideas, Baker's burden is truly heavy.