During his first year as governor of California, Ronald Reagan came under fire from a right-wing clique that objected to his accommodation of the Democratic majority in the state legislature on tax and budget issues.

Reagan turned the criticism to his advantage, realizing that it made him appear more moderate. Subsequently, he described the Republican legislator who led the attack as "a guy who jumps off the cliff with flags flying" to make a point.

"I'm willing to take what I can get," Reagan told me in a 1968 interview. "You have to take what you can get and get some more next year; that's what the opposition has been doing for years."

Reagan's incremental approach prompted aide Lyn Nofziger to label him "a Fabian conservative" in a shrewd comparison to the 19th-century English socialists who advanced a radical program a step at a time, working peacefully through the political system.

And that is exactly what Reagan has been doing for the past two decades. On issues that matter most to him, Reagan has been willing to settle for small bites of what he wants and come back to Congress for the rest of the meal.

For five years Reagan has been trying to browbeat or cajole Congress into assisting the Nicaraguan rebels he calls "freedom fighters." The rebels, or contras, have little public support and less prospect for military success. But Reagan believes in their cause, and he has nickeled-and-dimed Congress into keeping a semblance of aid flowing to the contras. If Congress rejects his present proposal to provide a transfusion of military aid to the rebels, no one doubts that Reagan will return with another request.

Since the 1940s, when he started making money as a movie actor at a time when marginal tax rates were high and individuals could not average income, Reagan has been obsessed with the idea of lowering federal income tax rates and reducing the revenues of government. He still is. The Senate, under administration prodding, now seems likely to pass a progressive measure that lowers individual tax rates and raises corporate rates. Should the Senate version prove unacceptable to the House, you can bet the mortgage that Reagan will try again in 1987 for tax reform.

Reagan also has resisted pressure to seek new taxes while lowering individual rates. Last week the president politely warned Senate Finance Committee Chairman Bob Packwood (R-Ore.), architect of the Senate tax-overhaul measure, that he was prepared to veto a bill that was not "revenue-neutral."

What makes Reagan formidable as a political leader is that he is willing to accept small gains without abandoning his persistent fealty to an ambitious agenda. He is simultaneously a trimmer and an ideologue, and it pays dividends.

Reagan came into office determined to raise the level of military spending, reduce taxes and balance the federal budget. He sacrificed the last objective to achieve the first two, but he has not given up on his goal of shrinking government growth at the expense of domestic programs. His latest budget proposes more than $10 in domestic spending savings for each dollar of savings in military spending. Reagan will have to compromise, but his agenda has once again defined the fiscal debate.

To a large measure Reagan's agenda is inner-directed. Certainly it does not derive from public opinion polls, which show a consistent disinterest in Nicaragua and a yawning unconcern with overhauling the tax system. On the latter issue, the greatest intensity comes from business interests, which contribute mightily to Republican candidates and actively oppose tax reform.

Reagan continues to plow ahead. His rhetoric sweeps, while his policies nibble. Sophisticated complexities elude him, and he makes no pretense of burning the midnight oil. At times he seems so distanced from the day-to-day execution of administration policies that it is difficult to trace their relationship to the Reagan agenda.

But it is ideas and purpose that ultimately prevail, and Reagan knows what he wants. At 75, in the sixth year of his presidency, he is truly a Fabian conservative who will take whatever Congress gives him. After that he will come back for more.

Reaganism of the Week: Asked last Wednesday his reaction to daughter Patti Davis' autobiographical novel "Home Front," the president said: "I hope she makes a lot of money. I thought it was interesting fiction."