MADRID, Spain: It's not easy getting into club NATO . Just ask Romania and Slovenia. Today, the military alliance turned up its nose to the former Soviet bloc countries and invited Poland, Hungary and the Czech Republic to join the clique. According to the expansion plan, the three nations are slated to become official members by the year 2000. In the days preceding the final decision, France had led the charge for a bigger freshman class, but the United States and Britain blocked the idea, maintaining that expansion should occur at a modest pace. That should soothe Russia, which opposes the expansion. But President Clinton must also convince the Senate that enlargement is good for the U.S., a tricky task considering that a bigger NATO will put American taxpayers out at least $200 million more per year. TIME's Bruce Nelan says to expect a knockdown drag out fight in the Senate. "Most of the senators haven't focused on it yet. But as the debate moves on and we near a vote in about a year, the topic will have been rehearsed a lot more and people will be more aware of what the costs, risks and question marks are. Already, 20 senators have written a letter to the President asking some very serious questions about why this is being undertaken. So while it's not exactly clear what the overall outcome will be, indications are there will probably be a very serious tussle."