WHEN Fidel Castro Ruz made his last visit to the United Nations, he was the object of a rare consensus in Washington. The only way to deal with his threatening, Soviet-backed regime, Republicans and Democrats agreed, was to isolate and strangle it.
Sixteen years later - with another UN visit in the offing - the consensus has evaporated. With the Cuban leader weakened and vulnerable, politicians now debate whether tightening or relaxing economic sanctions will bring his rule to the quickest end.
''There are two philosophical roads you can go down: The best way to undermine Castro is either to ease up on the sanctions and flood Cuba with capital or to deny Castro hard currency,'' says a congressional source. ''After that, you're debating tactics.''
At this writing, Mr. Castro had not yet been granted a visa to attend 50th anniversary celebrations at the UN later this month.
Conservative lawmakers oppose giving him a visa on the grounds that he is a sponsor of terrorism and will use his trip to lobby against continued United States economic sanctions.
A senior administration official responds that under the agreement establishing UN headquarters in the US, ''it would be hard to imagine denying a visa to a head of state.''
The White House and Congress agree that with the Soviet Union gone and communism in disrepute, Castro is living on borrowed political time. The question is how to shorten it.
Anti-Castro hawks in Congress, including Senate Foreign Relations Committee chairman Jesse Helms (R) of North Carolina, say the US should tighten its sanctions, imposed in 1962, to finish off Castro's regime.
Many US businessmen reply that unilateral sanctions haven't worked. They advocate loosening the embargo to allow US firms to compete for business in Cuba.
PRESIDENT Clinton has a foot in both camps. He urges maintaining sanctions but also opening Cuba wider to the contagious idea of democracy.
The debate was stirred again last Friday when Mr. Clinton announced that he would permit US news organizations to establish bureaus in Cuba and allow Cuban journalists to work in the US. A presidential executive order also eases restrictions on travel for educational, cultural, human rights, and religious purposes and directs the attorney general to step up enforcement of the embargo.
Senate majority leader Bob Dole (R) of Kansas denounced the measures as the latest step toward normalizing relations with the Castro government - an allegation the administration denies.
Senator Helms, author of a bill to stiffen US sanctions on Cuba, takes a more benevolent view, according to one aide.
''What the president did last week was to reject the advice of people who have been lobbying for more than a year to ease the embargo,'' says committee spokesman Marc Thiessen. ''We saw that as a philosophical endorsement of the Helms bill.''
''We do accept the argument that it is pressure and denial of resources that is necessary as an overall Cuba policy,'' acknowledges the Clinton official.
But the official says the Helms bill and a companion measure sponsored by Rep. Dan Burton (R) of Indiana and approved by the House last month lack the flexibility needed to bring Castro's reign to a speedy end.
''Our problem [with the Helms-Burton legislation] is that it is all pressure and no opening to the Cuban people,'' the official says.
The official compares the Clinton approach to Cuba to the ''Ostpolitik'' (Eastern policy) of West Germany, which warmed relations with Soviet-bloc nations during the cold war. But while Ostpolitik was based on government-to-government ties, the official notes, Clinton's policy represents an opening to the Cuban people.
The Helms and Burton bills urge the president to seek a UN embargo on - and to block international loans to - the island nation. It would also ban sugar imports from countries that import sugar from Cuba and allow Cuban-Americans to file lawsuits in US courts against foreign companies using expropriated assets.
Mr. Dole has promised to bring the Helms bill to an early vote. Clinton wants to maintain sanctions, but has threatened to veto the legislation, in part because of its secondary-boycott provisions.
Castro has visited the UN twice before, in 1960 and '79. He is scheduled to address the General Assembly on Oct. 22.