Communications Satellite Corp. yesterday proposed steep rate reductions for use of international satellites to transmit television and telephone signals.

If approved by the Federal Communications Commission, the new charges would apply across the board and would represent "the largest overall reduction in the history of international satellite communications," the Washington company stated.

The proposed decreases would take effect Aug. 10, unless the FCC permits an earlier date, Comsat said. Lower international rates were required as part of an agreement between Comsat and the FCC announced earlier this year to end a long dispute that began in December 1975 when the regulator agency ordered Comsat to reduce rates.

Television rates, which currently range from $404 to $725 for the first 10 minutes, would be slashed to $275. Additional per-minute charges would be $10 compared with a current range of $11.40 to $20.50.

For voice communications channels, Comsat has proposed a single rate of $1,575 a month to lease a channel between the U.S. and foreign points compared with a current range of $2,500 to $4,900 a month.

The rate for satellite channels between the mainland and Puerto Rico would be cut to $970 a month from $1,500. A previous practice of charging higher rates for Pacific Ocean transmissions than across the Atlantic also would be eliminated.