The agreement, the result of more than a year of negotiations, was announced by Sens. Richard G. Lugar (R-Ind.) and Barack Obama (D-Ill.) during a visit to the Ukrainian capital, Kiev. The senators credited Ukraine’s reformist leaders, ushered into power by last fall’s Orange Revolution, with breaking bureaucratic resistance to the pact.

One lab to receive funding is the I.I. Mechnikov Antiplague Scientific and Research Institute, in the Black Sea port city of Odessa. The institute was part of a Cold War network of “antiplague” stations that supplied highly lethal pathogens to Soviet bioweapons factories.

“This agreement will allow us to begin addressing the problems faced by the Odessa antiplague institute and places like it,” said Mark Helmke, a staff member for the Senate Foreign Relations Committee, which Lugar chairs. Under the pact, the United States will fund security upgrades at key Ukrainian biological institutes and support peaceful research by Ukrainian scientists to fight the spread of natural diseases, Helmke said. The amount of funding has not been determined.

The senators’ visit to Russia and Ukraine was disrupted Sunday when local authorities refused to allow the delegation’s military plane to leave Perm, a city in Russia’s Ural Mountains. The officials demanded that they be allowed to search the plane, then relented after several hours and allowed the aircraft to proceed to Ukraine, a spokesman for Lugar said. Yesterday, Russia’s Foreign Ministry formally apologized for the incident.

Viktor Yushchenko, left, the president of Ukraine, greets Sens. Richard G. Lugar, center, and Barack Obama during their visit to the capital, Kiev.