Air cargo service to Mexico is becoming more competitive.

The latest entrant, DHL Worldwide Express, began weekday overnight service about two weeks ago.Airborne Express, through a forwarder partner, inaugurated similar service late last year.

Last September, U.S. officials selected Evergreen International Airlines, Federal Express Corp. and United Parcel Service Inc. to provide service to Mexico. Evergreen subsequently withdrew its bid. This will allow Amerijet International of Fort Lauderdale, Fla., to begin service.

The largest single shippers to and from Mexico are the Big Three automakers that recently established "twin" plants there.

DHL's flight goes from Mexico City to Monterey and on to Houston each weekday night. DHL uses the airport in Mexico City; most competitors serve Toluca, an airport about 25 miles from the center of the Mexican capital.

In Houston, the DHL flight, a Boeing 727, meets a connecting DHL flight that originates in the company's Cincinnati hub. It collects freight there that originated throughout the DHL system, said Glen C. Gates, director of charter and contract services.

DHL is soliciting additional freight forwarder traffic to boost profitability of the Mexican run. The DHL plane is owned and operated by Taesa, its Mexican partner. It's painted, however, in DHL livery.

Over time, DHL envisions the Taesa flight traveling directly to its Cincinnati hub.

Airborne feeds traffic from throughout its system to Pegaso, one of Mexico's largest express companies, in San Antonio.

Pegaso charters a small business jet that carries the packages to Toluca and distributes them throughout Mexico.

This effort is Airborne's second. For several months in early 1989, Airborne flew its own DC-9 to Toluca.

It subsequently discontinued the service because it wasn't profitable, Airborne officials said.