CHICAGO (AP) _ The first night trading session in the history of a U.S. exchange drew about 500 traders to the floor of the Chicago Board of Trade Thursday evening.

''It's like the start of the baseball season,'' said arbitrage trader Keith Aarseth of Chicago Research and Trading.

''It's a real healthy beginning,'' added Bill Murschel, an exchange spokesman.

Since exchange officials approved plans for the night sessions in January, traders have been devising ways to work the extra three-hour session.

By extending the trading hours, exchange officials hoped to garner a bigger share of overseas business and compete with foreign exchanges and banks offering products that imitate futures contracts, they said.

The new hours coincide with morning trading sessions in Tokyo and the Far East, where investors have bought significant holdings in U.S. Treasury bonds and notes over the past several years, the officials said.

Traders wearing ''Night and Day'' pins on their blazers yelled bids and offers Thursday night across a trading floor that was usually empty at that hour.

Most of the activity was in T-bond futures contracts, exchange officials said.

At the end of the inaugural evening session, T-bond futures closed at 93.03, up 5.32 from the end of the day session, which closes at 2 p.m.

Exchange officials estimated the new session would cost about $1 million a year, which they hoped to offset with increased business, particularly from Japanese investors.