HELSINKI/WASHINGTON—Finland signed a $9.4 billion agreement on Friday to buy U.S. F-35 fighter jets, reaching a deal to bring 64 radar-evading warplanes to a country bordering Russia at a time of high tensions between Moscow and the West over Russian troops massed near the Ukrainian border. However it will be some years before the planes enter service. Finland has previously said the planes would begin to be deployed in 2027. In addition to the planes, the contract with U.S. government, and plane-maker Lockheed Martin includes maintenance equipment, spare parts, and training services, Finnish Defense Forces said in a statement on Friday, adding an agreement to buy air-to-air ammunition would be signed later in 2022. “The aim is to ensure that Finland’s F-35 system has the best possible performance going into the 2030s,” the Defense Forces said. Finland, which was historically neutral during the Cold War, is a member of the …