The president of Costa Rica got the Watergate Hotel, the prime minister of Israel got the Sheraton Washington Hotel. Meanwhile, Blair House, where one or the other of them might otherwise have stayed this week on their official visits here, got ready for renovations.

For Costa Rica's Luis Alberto Monge, the Watergate was also the setting last night for a dinner he gave as part of his three-day lobbying effort to obtain financial help for his country. With inflation at 90 percent and the country near bankruptcy, Costa Rica has more than a casual interest in the Reagan administration's controversial Caribbean Basin plan which would provide it with $70 million in emergency aid as well as trade benefits.

Rep. Henry Reuss (D-Wis.), who heads the House Joint Economic Committee and was one of a half-dozen members of Congress at Monge's stag dinner, saw some reciprocal benefits in the Costa Rican leader's visit.

"We're sort of lobbying him because Costa Rica has no illusions about communism. It's a strong human rights democratically oriented country," said Reuss, "so this may be another case like Jamaica, where the Democrats and the Reagan administration can agree on something."