As Congress neared the end of its session at press time, lawmakers were considering at least two proposals on "conflict diamonds"-including one that could halt all diamond imports into the United States. The proposal, a rider attached to a congressional spending bill by Senator Judd Gregg (R-N.H.), says no diamonds from conflict areas can be imported into the United States. Since there is now no way to determine a "conflict" stone, Customs Service officials may decide that the only way to follow the law is to stop all diamond imports. They may also decide to ignore it as unenforceable. "We won't know until Customs decides," says David Rocha of Jewelers of America. The Gregg rider passed Congress, but the overall spending bill is likely to be vetoed by President Clinton because of some unrelated provisions on immigration. There is, however, a slight chance that the disputed immigratio