wo major downtown transportation projects related to the rebuilding of the World Trade Center got under way this week as officials issued requests for proposals from companies seeking to work on the projects' early stages.

The Lower Manhattan Development Corporation and the Port Authority of New York and New Jersey are seeking a consultant to conduct a six- to nine-month study of alternatives to link Lower Manhattan with both Kennedy International Airport and Jamaica Station on the Long Island Rail Road.

The selected firm will review several long-term alternatives for achieving the links, including the possible construction of a new tunnel under the East River, new connections between city subway lines and the AirTrain at Kennedy Airport, and the use of subway tracks to connect downtown with the Jamaica station.

Short-term options, including new ferry routes to the airport, will also be studied. The long-term projects are intended to be completed by 2013.

The Port Authority also issued a request for proposals from architectural and engineering companies to oversee planning and construction of the new transportation hub at the trade center site.

The winner of that contract will complete architectural and engineering work on the terminal, following design guidelines laid out by Studio Daniel Libeskind. Mr. Libeskind's firm is developing the master plan for the trade center site as well as specific guidelines for the terminal, which the Port Authority describes as "a fully developed, regional transportation hub."

The building will serve the PATH commuter trains and the several subway lines that run close to the trade center site, as well as connect to the planned Fulton Transit Center via an underground concourse.