The Senate, closing the first chapter of the 100th Congress' effort to put a Democratic imprint on the nation's spending policies, yesterday endorsed a $1 trillion budget for fiscal 1988, amid Republican predictions that it will never take effect.

The spending blueprint, negotiated last week by a House-Senate conference committee and adopted on Tuesday by the House, calls for $19.3 billion in new taxes and virtually no increase in defense spending unless President Reagan abandons his pledge and does not veto tax increase legislation.

The budget, covering the federal spending year that begins Oct. 1, passed the Senate 53 to 46, with three Republicans voting for the budget resolution and three Democrats opposing it.

With the approval of the budget last night, Congress now embarks on the more difficult task of enacting the individual spending and revenue-raising measures necessary to translate the framework into policy. To do so, the Democrats, who now maintain a tenuous control of Congress for the first time since Reagan took office, must negotiate a gauntlet of presidential opposition.

"Without the president's cooperation and positive involvement, the next few weeks will not be easy," Senate Budget Committee Chairman Lawton Chiles (D-Fla.) conceded yesterday. "I ask again for the president to join us."

But the White House officials, convinced that the best way for the president to recapture the momentum he has lost in the Iran-contra affair is for him to lambaste the "tax and spend" policies of the Democratic Party, show no signs of conciliation.

And, as they have increasingly done in the past two months, most Senate Republicans showed during yesterday's debate on the budget that they are eager to follow Reagan's lead. Though outnumbered in the Senate 54 to 46, Republicans have sufficient votes on many issues to uphold presidential vetoes, and they appear convinced that their best hope of retaking control of the Senate in 1988 lies in using that muscle to stymie the Democratic program.

"This is a budget that goes a long way to repealing the Reagan economic program," said Sen. Phil Gramm (R-Tex.), echoing the rhetoric the president has used in recent days in a highly visible campaign to portray Democrats as undisciplined spenders and taxers. "We are not raising taxes here to lower the deficit, we are raising taxes to increase spending."

In an assault on the Democratic budget, other Republicans charged that the spending plan would leave the nation's defenses as vulnerable as they were during the administration of President Jimmy Carter and would raise taxes to fuel an increase in domestic spending.

"This budget holds our national security hostage to a tax increase," Sen. Pete Wilson (R-Calif.) said.

The Democratic budget calls for defense spending authority of $296 billion, $16 billion less than Reagan requested. However, if the president does not sign separate legislation containing the $19.3 billion tax increase, military spending authority would drop to $289 billion. Without presidential acceptance of the tax increase, Pentagon outlays in fiscal 1988 would be nearly frozen at current-year levels.

Democrats countered the Republican assault with reminders that Reagan -- for all his promises to balance the budget, cut spending and shrink the government -- has failed to deliver and has left the country perilously in debt. The Democratic budget -- calling for $64 billion in new taxes over three years and for a growth in domestic spending that is less than inflation -- they argued, is a responsible way to chip at the federal deficit, which this year will total around $171 billion.

"This is the president who rode into town in 1981 preaching the virtues of a balanced budget while condemning the fiscal waste and unhealthy deficits of prior administrations," Sen. Terry Sanford (D-N.C.) said. "Today, six years later, the nation is drowning in a sea of red ink from his policies, which have yielded the six largest budget deficits in our nation's history."

"This is the president who states that he will bear full responsibility for his actions and yet this is the same president who always seems to find a fall guy for the bad things that happen on his watch," Sanford said.

The Democratic budget, if fully implemented, would reduce the deficit by $37 billion but would still miss the $108 billion deficit target set by the Gramm-Rudman-Hollings law by about $26 billion.