In the waning days of Congress' preelection session, several key links in the Washington area's transportation network -- among them National Airport, the Metro system, the Whitehurst Freeway and the region's two biggest ports -- have gotten carried along by the legislative express train.

To the dismay of many Northern Virginia officials, the Senate has moved to block the U.S. Department of Transportation's proposal to lower the ceiling on the number of passengers using National Airport. Some officials had hoped a lower cap might help reduce aircraft noise and other problems.

Local officials were delighted, however, as the Senate acted to overturn the Reagan administration's 76.4-mile limit on Metro construction. The move, they said, could clear the way to expand the rail system, including major parts of the long-stalled Green Line in Prince George's County.

District officials have pointed with alarm this week to a controversial amendment to a massive highway bill, warning that it could wipe out funds for a $100 million overhaul of the deteriorating Whitehurst Freeway on the Georgetown waterfront.

Yesterday, the Senate passed a measure designed to provide start-up funds for huge dredging projects at the Baltimore harbor and Virginia's Hampton Roads port to deepen both ports to accommodate large coal ships.

Two Virginia Republicans, Rep. Frank R. Wolf and Sen. John W. Warner, announced 11th-hour moves yesterday to try to head off billions of dollars in lawsuits against the Metro system by subway construction workers who suffered injuries or ailments on the job. Metro previously appealed for help.

With Congress entangled in intricate last-ditch maneuvering over many issues, prospects for the measures -- those benefiting or buffeting local projects -- were difficult to gauge. Nevertheless, officials said the National Airport and Metro construction measures are expected to pass.

In her first statement on the Senate move, Secretary of Transportation Elizabeth Hanford Dole said yesterday she opposes the National Airport measure. Dole proposed last June to lower the airport's cap to 15.2 million passengers a year, 800,000 below the current ceiling.

The Senate measure, attached to a catchall spending bill, "would prejudge" the issue and "precludes the kind of detailed, careful scrutiny" that is needed, Dole said.

Advocates of the Metro construction measure said it could help prod the Reagan administration to approve a new plan calling for completion of 89.5 miles of the proposed 101-mile system with funds previously authorized by Congress. Dole has praised the plan, but stopped short of endorsing it.

The proposed Whitehurst Freeway overhaul is jeopardized, according to D.C. officials, by a highway amendment that would siphon off a sizable share of federal funds for projects in Illinois, leaving some other areas short of money. The District wants to use those funds to renovate the freeway, starting in late 1986.

The Wolf and Warner proposals to head off lawsuits against Metro are expected to be attached to some other measure later this week. They are aimed at countering another bill, recently signed by President Reagan. Officials said the earlier legislation had the effect of nullifying a recent U.S. Supreme Court decision and has left Metro vulnerable to hundreds of lawsuits.

The port measure, attached to the catchall spending bill, would provide $18 million for Baltimore and $10 million for Hampton Roads. Prospects are uncertain, however, because the Senate has not agreed to a formula for distributing the money.