Fares on District of Columbia taxicabs making interstate trips will rise 30 cents at 4 a.m. Monday.

In an announcement just published, the Washington Metropolitan Area Transit Commission said the new fares for typical trips will be close to those already charged by suburban taxicabs. Only the rates charged by Montgomery County cabs will remain substantially higher.

A study of the higher rate was begun by the commission shortly before the D.C. Public Service Commission granted the cab industry a rate increase within the city that took effect Oct. 7. Fares within the District went up 15 cents for a downtown one-zone trip and 45 cents for a four-zone trip from downtown to the city's outer edges. t

Under interstate agreement, the transit commission controls the rates for cab trips across the District line. It has adopted the metered rates set by cabs licensed in the Maryland and Virginia suburbs. Since D.C. cabs follow a zone system and lack meters, the commission must set rates for them in separate proceedings.

Rather than altering the price charged per mile, the commission simply added 30 cents to each individual fare.

For a five-mile ride, which would include many trips between the city and National Airport the present $4.40 fare will rise to $4.70; the fare for a 10-mile trip will rise from $8.40 to 8.70 and for a 15-mile trip, it will rise from $12.40 to $12.70.

In taking the action, the commission rejected proposals submitted independently of each other by two cab drivers, Jack B. Dembo and Irving M. Schlaifer. Both proposed rates averaging out to $1 a mile.

The commission said it never has been its policy to lead the way in setting higher regional cab fares, which the two drivers' proposals would have produced.

Under the new rate structure, the D.C. $4.70 rate for a five-mile trip will be above that of Fairfax County ($4.20), the same as Prince George's County, and just below the rates for Arlington and Alexandria ($4.80).

Montgomery County's rates are the highest, $5.10 for five miles and $14.10 for 15 miles.

The commission said it is now considering an increase from 60 cents to 75 cents for a second passenger accompanying the basic farepayer on an interstate trip.