With the boom in subway and bus ridership showing no signs of abating, transit officials said Wednesday that they planned to spend $44 million to expand service over the course of 1999.

The plan, which is to be announced Thursday, will add 2,400 bus trips and about 200 subway trips a day to a system that after two years of dizzying growth in ridership is often packed to capacity.A transit official, speaking on condition of anonymity, said that the $44 million expenditure, combined with the $65 million that has been spent the past two years to gradually add new service, "is the largest increase in service that we can find in our records." The increases follow closely on the heels of $48 million a year in service cuts imposed by the authority in 1995 after the city withdrew $112 million in subsidies.

Under the plan, service will increase on 17 subway lines, including the No. 1 line in Manhattan and the A train. The transit official said that both those lines were not only overcrowded during peak hours, but were also increasingly crowded before and after the traditional peak.

Service will also increase on the No. 7 line, which is growing more crowded on weekends and during other off-peak hours. In addition to more express bus service between Manhattan and Staten Island, Brooklyn and Queens, the plan calls for extra crosstown bus runs in Manhattan and increases on several lines in the Bronx and Queens.

The added service, officials said, will reduce waiting times on some subway lines by a minute or so during during peak travel times and by two or three minutes during off-peak times.