U.S. Senate leaders have abandoned their efforts to override President Bush's veto and introduced a new bill to reauthorize Amtrak and clear the way for Northern Virginia's first-ever commuter rail service to the District.

Earlier this week, the Senate failed to muster the two-thirds vote necessary to override Bush's veto of the bill, but Majority Leader George J. Mitchell (D-Maine) asked the Senate to reconsider the vote at a later date. Bush had objected to a provision in the bill that required the Interstate Commerce Commission to review acquisitions of freight railroads by non-rail companies.

Sen. J. James Exon (D-Neb.) formally withdrew the motion for reconsideration yesterday when he introduced the new bill, which is almost identical to the old one minus the ICC provision. The Senate is expected to act by early August.

House leaders are negotiating a plan for speeding passage of a new version of the bill, which has been introduced by Minority Leader Robert H. Michel (R-Ill.).

The commuter rail provision would exempt the Consolidated Rail Corp. from liability in an accident. Without the legislation, Conrail will not let the Virginia Railway Express use its D.C. tracks, and passengers coming in from Manassas and Fredericksburg would have to transfer to Metro in Alexandria to get into Washington In that case, the projected ridership would drop from 4,000 round-trip passengers daily to 2,680.

The railway is expected to begin service in October 1991.