(Adds Kosovo president, prime minister; EU envoy Feith)

By Matt Robinson and Shaban Buza

PRISTINA, April 9 (Reuters) - Kosovo adopted a state constitution on Wednesday, which will come into force in mid-June when the United Nations completes a handover of powers to the newly independent country and its EU overseers.

Parliament endorsed the document without a vote, almost two months after the 90-percent Albanian majority declared independence from Serbia with Western backing.

It declares Kosovo a secular republic, "an independent, sovereign, democratic, unique and indivisible state".

Kosovo expresses its determination "to build a future ... as a free, democratic and peace-loving country that will be a homeland to all of its citizens", the text reads.

The constitution will come into force on June 15, when the U.N. mission that has run the former Serbian province since 1999 is due to hand over its remaining powers to Kosovo's ethnic Albanian leaders and new EU-led supervisors.

But questions remain over how the transition will proceed, after Serb ally Russia last year blocked the adoption of a U.N. Security Council resolution endorsing the EU takeover and a U.N. plan for independence.

Prime Minister Hashim Thaci, who fought in the 1998-99 guerrilla war against Serbia, told parliament: "The constitution clearly defines our hope, our optimism, our belief and our rights, which are strongly supported and keep us united."

President Fatmir Sejdiu appealed to Kosovo's 120,000 remaining Serbs to accept the document, and to become a "bridge" between Kosovo and "our neighbour, Serbia".

UNITED NATIONS

The U.N. mission says it is "awaiting instructions" from headquarters on how to proceed with what U.N. officials now describe as its "reconfiguration" rather than transition.

It is certain to remain in some form, and retain some powers, under Security Council resolution 1244.

Kosovo's new EU governor, International Civilian Representative Pieter Feith, said on Monday he needed "more visibility" on which powers the U.N. mission would retain.

"The U.N. may wish to exercise powers to do with issues like foreign representation of Kosovo under 1244, travel documents, things like that," Feith told Reuters.

Kosovo already runs most of its own affairs, but the constitution also creates a Foreign Ministry, Defence Ministry, security force, constitutional court and intelligence agency.

The text includes extensive provisions for the protection of the Serb minority, under the U.N. plan for "supervised independence" that was rejected by Russia but backed by Kosovo Albanians and the major Western powers.

Serbia lost control over Kosovo in June 1999 when NATO bombs drove out Serb forces to halt the killing and ethnic cleansing of Albanians in a two-year counter-insurgency war.

Kosovo has been recognised by more than 30 countries, including the United States and most of the 27 EU member states. But Serbia rejected the Feb. 17 secession. It is supporting a Serb boycott of the new state, deepening its de facto partition.

It remains unclear how Feith's supervisory office and the 2,000-strong EU police and justice mission will deploy in the mainly Serb north, where hostile Serbs reject the takeover. (Additional reporting by Fatos Bytyci; Writing by Matt Robinson; Editing by Alison Williams)

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