President Reagan is racing toward a collision with Congress on foreign and domestic policy fronts this week. By vetoing a bill to impose economic sanctions on South Africa Friday, the President has set himself up for a rare confrontation with Senate Republicans, a majority of whom voted for the legislation earlier this month. Mr. Reagan will face the steepest odds of his presidency if he attempts to persuade Congress to accept his package of less-severe sanctions in place of the tough sanctions bill he vetoed.
Then, on Saturday, Reagan threatened to close down the federal government if Congress does not prune pet programs and ``simply unacceptable'' arms control restrictions from a massive spending bill designed to keep the government running. The legislation contains money needed to fund key federal programs. Lawmakers are rushing to put the bill together as the clock ticks away the final hours of fiscal 1986, which ends at midnight tomorrow.
The President bemoaned Congress's failure again to pass its 13 regular appropriations bills on time.
``If [lawmakers] don't act responsibly, I won't have any choice but to shut [the federal government] down,'' Reagan said in his weekly radio address. ``If they want to put a real budget together by candlelight, it's OK by me.''
Meanwhile, the House of Representatives is scheduled to vote tomorrow on whether to override the presidential veto of the sanctions bill, while the Senate is supposed to take up the same question Wednesday.
Both chambers approved the sanctions bill by more than the two-thirds majority needed to override a veto. Congressional observers say it is virtually impossible for the President to gain the necessary votes in the Democratic House to sustain his veto.
His best hope -- and, say lawmakers, a faint one at that -- is in the Republican-controlled Senate, where 14 members voted to support Reagan when the legislation was debated.
But Senate Foreign Relations Committee chairman Richard G. Lugar (R) of Indiana, who has broken ranks with the White House over sanctions, said on Friday that the administration has only 25 or 30 of the 34 votes it would need to sustain a veto if all senators voted. (Congress has voted to override five presidential vetoes during the Reagan administration.)
Nevertheless, administration officials reportedly believe the battle to sustain the veto can be won. Reagan is suggesting that he would agree to impose new sanctions against South Africa's white-minority regime along the lines of those approved recently by the 12 nations of the European Community.
At the same time, no one discounts Reagan's capacity to snatch victory from the jaws of near-certain congressional defeat.
A few political observers say they believe it may be difficult for some Republican senators in tight reelection races to say no to the popular President, particularly if they hope for a presidential campaign appearance in their home states before election.
Senate majority leader Robert Dole (R) of Kansas, who supported the sanctions bill the first time around, urged his colleagues to sustain the veto. A stronger message would be sent, he said, ``if the President and the Congress could speak together'' and work out a sanctions compromise.
At the same time, a sanctions bill opponent, Sen. Larry Pressler (R) of South Dakota, noting that the Senate hopes to adjourn Oct. 4, said he might try to stall the Senate override vote with a filibuster.
But many lawmakers still say such steps would probably not be enough to overwhelm the anti-apartheid sentiment in Congress, which propelled members to support a bill that includes a ban on all new United States investment and bank loans in South Africa, applied in hopes of pressuring Pretoria to abandon its system of racial segregation.