The fiscal 1987 budget approved by the Senate last week -- the first to top $1 trillion, the first to pass either chamber under Gramm-Rudman-Hollings deficit constraints and the first in years to carry a real bipartisan label -- is remarkable largely for what it is not.

When the Gramm-Rudman-Hollings deficit reduction act was passed last year, there were dire warnings of chaos: Congress, it was said, was unlikely to come up with a budget that could meet the deficit targets, and, if it did, the result was likely to be so severe that the government would virtually dry up and blow away.

The Defense Department would be cut so heavily that national security would be jeopardized; social welfare spending would slow to a trickle; taxes would be put off-limits; partisan strife would be rampant; paralysis would lead to across-the-board spending cuts, required by the new deficit reduction rules when Congress cannot meet the targets on its own.

But with a timely assist from the economy and a little creative number-juggling, the Senate, after a lot of political wheezing and groaning, found that complying with Gramm-Rudman-Hollings was not all that wrenching an ordeal.

Basically, it nibbled here, there and everywhere, producing a budget with a sufficiently even distribution of pain and pleasure that it passed by an unprecedented bipartisan vote of 70 to 25, supported by senators spanning the political and philosophical spectrum from Strom Thurmond (R-S.C.) to Edward M. Kennedy (D-Mass.).

It met the $144 billion Gramm-Rudman-Hollings deficit target for the next fiscal year by setting spending and tax targets to achieve $39 billion in deficit reductions, including $2 in spending cuts for every $1 in new revenue.

As might be expected from a Republican-controlled legislative body, it held to the broad outlines of President Reagan's six-year drive to limit the government's taxing powers and shift its resources from the domestic to the military side of the ledger.

But, with Democratic cooperation necessitated by a virtually crippling division within GOP ranks over tax policy and spending priorities, it did so far less faithfully than in previous years.

Taxes would be increased marginally, with a $13.2 billion rise (including cigarette and other levies already enacted) accounting for little more than 1 percent of total revenues of $857 billion for next year. In all, taxes would be increased by a cumulative total of about $50 billion over three years. It would be up to the tax-writing Senate Finance Committee and House Ways and Means Committee to decide what taxes are to be raised; budget drafters made it clear that they did not intend for the new revenue to come from income taxes.

Defense spending authority would grow by far less than the administration wanted but by more than enough to cover inflation, once again making the Pentagon the first among equals when it comes to spending.

Reagan's defense request of $320 billion was trimmed to $301 billion, an increase of about 5 percent over current spending authority of $287 billion, or more than enough to cover anticipated inflation of about 3 percent. It would be the second year in a row that Congress basically held the line on limiting defense increases, following big increases in the military budget during Reagan's first term.

Most domestic spending would be frozen at current levels, but some high-priority programs, such as law enforcement and public safety, would be expanded. A few others, such as health and education, would be given at least enough to keep pace with inflation.

Instead of targeting specified programs for termination -- Reagan wanted to kill 44 programs, a list that the Senate Budget Committee reduced to three, and the Senate as a whole to two -- the Senate mandated unspecified savings spread out over the budget that could come from spending cutbacks or "possible terminations." Revenue sharing with local governments is one of the two programs to be terminated, but it had already been slated to end this year. Also, Conrail would be sold, although arrangements for the sale are in some doubt.

Except for subsidized housing and a few others, social welfare programs aimed primarily at the poor are shielded from deep new cuts, having borne the brunt of cutbacks in early years of the Reagan administration.

The relatively small work incentive program that provides job-related assistance for welfare recipients was a case in point. Targeted for extinction by Reagan and the Budget Committee, it was rescued at the last minute by the Senate, which appeared to have no stomach for killing any domestic programs, especially in an election year.

By contrast, foreign aid took a multibillion-dollar cut, despite the Reagan administration's pressure for increases above current program levels for military and economic assistance. As approved by the Senate, projected foreign aid and related spending of $14 billion was $1 billion below what it would take just to keep pace with inflation.

"It's clearly less harsh, particularly in social welfare and low-income programs, than most, if not all, previous budgets," said Robert Greenstein, director of the Center on Budget and Policy Priorities, a private budget monitoring group that has often criticized Reagan and congressional budgets in the past.

For a variety of reasons, including an impending Supreme Court ruling on the Gramm-Rudman-Hollings law's automatic triggering mechanism for spending cuts, it is far too early to tell how the first full year of the law will work out.

But for the moment, Gramm-Rudman-Hollings appears to have fostered discipline, bipartisanship and a sense of balance in budget cutting, which is new but hardly revolutionary. It was what Congress was supposed to be doing all along.