* Says interbank rate "unrealistic"
* Belarus maintains dual exchange rates
MINSK, April 21 (Reuters) - Belarus said on Thursday it was targeting a rouble exchange rate of 3,800-4,100 per dollar, much stronger than rates of around 5,000 seen since the central bank allowed the currency to float freely for trade between banks.
The rouble has lost more than a third of its value against the dollar on the interbank market since Belarus this week dropped restrictions on the exchange rate used by banks and companies, opening the door to a partial devaluation.
"Once we have a balanced exchange rate, we will work according to our plan of unifying the exchange rate," Deputy Prime Minister Sergei Rumas said on Thursday.
"In my opinion, this exchange rate is in the range of 3,800-4,100 per dollar. Today that fits in with the state of our economy," Rumas told Reuters.
Rumas called the current interbank rate -- around 5,000 roubles per dollar according to bankers -- "unrealistic".
The central bank kept the official exchange rate, used for mandatory export revenue sales and retail cashpoint operations, at 3,055 roubles per dollar on Thursday. It has said it will unify the two rates later.
Analysts say the rouble's plunge reflected a surge in demand from players who had been unable to buy dollars for weeks while the rate was regulated. Belarus has lost a quarter of its foreign currency reserves this year trying to support the rouble.
This week's developments have highlighted the currency problems of the ex-Soviet republic and are a setback for President Alexander Lukashenko, who is due to deliver his annual state of the nation speech later on Thursday.
Coming nine days after a bomb blast at a Minsk metro station that killed 13 people, the rouble's fall has added to the misery for Belarussian citizens promised better times ahead when Lukashenko was re-elected for a fourth term last December. (Reporting by Andrei Makhovsky; Writing by Olzhas Auyezov; Editing by Catherine Evans)