Senators will soon have an opportunity to demonstrate American solidarity with Great Britain in the resistance to terrorism. By chance, the proposed extradition treaty with Britain will be considered shortly after the British gave assistance and support to the American strike against Muammar Qaddafi.

Britain is this country's oldest extradition treaty partner. The original agreement dates to 1794, and was negotiated by John Jay. The treaty has been revised periodically, most recently last year when the parties agreed to supplementary language dealing with terrorism. The Senate has been asked to consent to ratification, and the Foreign Relations Committee, which has been studying the proposal for many months, is expected to act this week.

The problem with the current treaty is that it bars the extradition of persons whose crimes are political. It is quite possible, therefore, that the gang that bombed a Brighton hotel in an attempt to kill Prime Minister Thatcher, or the man who allegedly tried to put his girlfriend and 10 pounds of explosives on an El Al plane at Heathrow last week, would not, if they managed to get to this country, be returned to Britain for trial. U.S. courts, in at least four recent cases, have invoked the political offense clause in refusing to extradite people wanted in connection with violent crimes in England and Northern Ireland. The new language would deny sanctuary in this country to terrorists by defining the term "political offense" to exclude certain crimes such as murder, kidnapping, airplane hijacking and bombing. These are, as Americans well know, exactly the offenses most often associated with international terrorists, and it is easy to understand the importance of cooperating with allies in prosecuting them.

Some Democrats on the Foreign Relations Committee are balking at this agreement, and have offered alternative language. They would extradite only persons charged with offenses against civilians, which would presumably leave gunmen free to kill British soldiers and policemen at will. This is not unimportant, since that is what is now going on -- on both sides in the case of the police -- in Ulster and England right now. In these circumstances, the Democrats' proposal is seriously flawed.

The United States already has treaties with a number of countries that place some limits on the political offense exception, Canada and West Germany, for example, and Mexico, Colombia and the Netherlands, where the treaty leaves the definition of the term up to the executive branch. The United States has undertaken a cooperative effort with Britain to combat terrorism, and the ratification of this supplementary treaty is part of that effort. The Senate should ratify it.