Washington — In the early days of the 100th Congress, the controlling Democrats handed President Reagan a couple of swift defeats. But with a host of tougher challenges ahead, Congress will have trouble winning decisive victories, despite the Democrats' control of both houses. Aid to the Nicaraguan contras, arms control, the budget deficit, and other potentially divisive issues crowd the congressional docket as the Senate gets back to work today after a 10-day recess. It will be the task of the new Democratic leaders in both houses of Congress to forge a consensus on these matters.
The opportunities and potential pitfalls are heightened by an apparent sense of indirection at the White House.
Because of the seeming drift in the administration, the Democratic Congress could write the political agenda in the final months of the Reagan era. Or, with few White House initiatives to unite them in opposition, Democrats could take to quarreling among themselves, and enter the presidential election season bitterly divided on some pressing political topics.
Earlier this month, Republicans and Democrats readily joined forces to pass the Clean Water Act over President Reagan's veto, and despite White House opposition, both chambers passed transit bills that will go into conference. But these triumphs underscored the political popularity of clean water and transit programs, rather than the skill of Democratic leaders at organizing political opposition.
The issues now before the Senate, and the House of Representatives when it reconvenes next week, will test the ability of Democrats to settle on a consensus.
One major test will be the future of United States funding for the contras. The final $40 million installment of the $100 million in military and nonmilitary aid approved by Congress last year became available to President Reagan on Sunday.
The question for Democrats is whether they should try to bottle up the contra funds just now. President Reagan is expected soon to notify Congress of his intention to release the funds. Under last year's legislation, Congress has 15 days to block the funds by passing a resolution of disapproval.
President Reagan would almost certainly veto such a resolution. It is unlikely that opponents of the contra aid would be able to muster the two-thirds majority in both houses necessary to override the veto.
On the other hand, President Reagan has asked Congress for an additional $105 million in contra aid for the fiscal year 1988, which begins Oct. 1.
The Iran-contra affair has undermined support for the contras on Capitol Hill, reducing the likelihood that Congress will approve any new aid to the Nicaraguan resistance. Many Democrats believe they have a strong chance of defeating the President on next year's aid request, and are counseling aid opponents to hold their fire on the $40 million.
But other Democrats, such as Sen. Christopher J. Dodd of Connecticut, are counting votes to see if there is sufficient support to pass the disapproval resolution.
If there is, staff members say, the Democrats are likely to seek a vote on the resolution to demonstrate their political muscle, even though President Reagan would ultimately prevail on a veto.
Democrats are also being tested on arms control issues. Arms control advocates have been mobilized by a recent spate of White House actions. These include administration decisions to exceed arms limits established by the SALT II treaty, to continue nuclear testing at the Nevada test site, to consider a looser interpretation of the 1972 Anti-Ballistic Missile Treaty, and to speed up the timetable for deployment of elements of the Strategic Defense Initiative.
But Democrats have not had an easy time translating their political energy into legislative action. The Democrats' first arms control salvo was to take the form of Senate approval of two nuclear testing treaties, signed in the mid-'70s, limiting the size of nuclear explosions.
But President Reagan's request for a second vote on a tougher verification agreement to go with the treaties put the Democrats in a quandary. They wanted to approve the never-ratified treaties expeditiously, but they did not want to seem soft on arms control. So now the treaties are bottled up in the Senate Foreign Relations Committee, while chairman Claiborne Pell (D) of Rhode Island tries to negotiate a compromise with White House officials.
In other arms control areas, activity continues. Republican and Democratic senators have called for legislation to force compliance with SALT II limits, while Democrats in the House have introduced legislation aimed at halting all nuclear tests.
But other Democrats sense that a congressionally mandated test ban was last year's opportunity. The Soviet Union has stated that, in view of the US nuclear test Feb. 3, it will end its 18-month moratorium on testing.
The limits of Democratic political skills may be tested during this year's deliberations on the federal budget deficit. Reducing the deficit some $60 billion to reach the Gramm-Rudman balanced budget act's mandated target for fiscal 1988 will be a herculean task. President Reagan seems unlikely to budge from his opposition to tax increases to plug the deficit. So Democratic leaders say it is likely that the Gramm-Rudman targets will be changed or ignored.
There are bright spots for the Democrats, however. Both House Speaker Jim Wright of Texas and Senate Majority Leader Robert C. Byrd of West Virginia are emphasizing a similar agenda, focusing on education, farm, trade and ``competitiveness'' concerns, and welfare reform. Republicans and Democrats are cooperating on the early stages of the trade bill and aspects of welfare reform.