President Boris Yeltsin, clearly frustrated by failure to reach agreement with Estonia, has ordered Russian authorities unilaterally to demarcate the frontier with the Baltic state by the end of the year. Yeltsin, in a decree signed June 18 but published Tuesday, said the border must be clearly demarcated to protect Russia's political and economic interests. He accused Estonia of adopting a "negative attitude" to the issue. The frontier was completely open in Soviet times. But since the collapse of the Soviet Union, Russian authorities say, it has become a channel to smuggle out Russian goods. Controls are complicated because the frontier is not always clear. An Estonian Foreign Ministry spokeswoman said from Tallinn the decree could only add to tension over the presence of Russian troops. According to the decree, before conclusion of a bilateral agreement, the frontier would be that which existed when Russia recognized Estonia's sovereignty in August 1991. Estonia insists Russia should return the Pechory district by its southeastern frontier and a slice of land east of the Narva River, which belonged to it between the two world wars. Estonia was annexed by the Soviet Union in 1940 and some of its former territories remained under Russian rule after it regained its independence. Russia refuses to entertain discussion about the return of Pechory, which Estonia calls Petseri. Tallinn wants Russia's remaining 2,500 troops out by Aug. 31 but Moscow has linked the withdrawal with treatment of Estonia's 40 percent Russian minority. Moscow says language and citizenship laws discriminate against Russians, which Tallinn denies. Estonian Foreign Ministry spokeswoman Mari-Ann Rikken added: "We too would like a secure and normally functioning border but these things have to be done bilaterally." She said there was still time to talk. She said Estonia had proposed at the recent European Stability Conference that the issue be included in a round table on Baltic questions but Russia had refused.