EUROPEAN leaders took advantage of signs of disarray and confusion within the Soviet Union's newly declared leadership to strengthen their support for reformist forces resisting Monday's coup against Soviet leader Mikhail Gorbachev. The hardening of tone was reflected at Tuesday's emergency meeting of European Community foreign ministers, where the EC's aid program to the Soviet Union was suspended.Leaders of the European Community's 12 member countries are expected at an emergency EC summit tomorrow at The Hague to reinforce pressure in favor of continued economic and democratic reforms. This includes pushing for the Soviets to respect international agreements such as arms control and promised Soviet troop withdrawals in Europe. The summit is also likely to take up measures aimed at reassuring the Soviet Union's former satellites countries in Eastern Europe that the Community views as irreversible their attachment to a democratic and free-market Europe. After what was initially a surprisingly moderate response to Mr. Gorbachev's ouster by several European capitals, European leaders markedly hardened their tone. The change reflected at least two factors: One was an apparent reassessment of the West's ability to influence a still-fluid situation in the Soviet Union. The feeling was growing that a firm stand from the West can still sway Soviet events, and that Western support for the reformist resistance, including Russian President Boris Yeltsin and his backers, is crucial. On the economic front, the EC tomorrow could freeze progress towards a European energy pact, which was to open Soviet energy potential to European investment. It is a further attempt to influence Soviet action, this time through the purse. The change also reflects a willingness by Paris and Bonn to fall in line with the swifter, stronger reaction of Washington and London against Monday's coup. French President Francois Mitterrand said in a televised speech Monday night that economic sanctions were "premature," but by Tuesday French Foreign Minister Roland Dumas was saying, "The hour has come to pass judgment on events in the Soviet Union." Nervous German leaders, who Monday appeared to adopt a wait-and-see attitude, by Tuesday were calling for Mr. Gorbachev's return to power. At the emergency meeting of EC foreign ministers, $400 million in emergency food aid alone was exempted as the rest of the $1.15 billion assistance package, agreed last December for the Soviets, was put on hold. Saying the return to power of Gorbachev would be "the best proof of a return to legality," Dutch Foreign Minister Hans van den Broeck, the EC president, explained his colleagues' call for Gorbachev's reinstatement and the right to visit him. Viewing warily the seizure of power in Moscow by forces that blame Gorbachev for the "loss" of Eastern Europe, EC leaders appeared abruptly awakened to a need to more strongly assist Central and Eastern European countries seeking to join the West. German Foreign Minister Hans-Dietrich Genscher called for accelerating the process through which Eastern European countries may gain EC associate status. Even EC Commission President Jacques Delors, until now an implacable supporter of "deepening" Community political and economic integration before "widening" beyond the current 12 members, this week indicated a change of position. Referring to the difficult negotiations that have followed Com-munity leaders' strong rhetorical commitment to Eastern Europe, Mr. Delors promised "reasonable and realistic" EC concessions in agriculture, coal, steel, and textiles. The Community can no longer "make fine speeches on Sunday" only to later in the week "oppose the trade concessions enabling those countries to sell their goods and improve their standards of living," he said.