Metro officials expressed concern yesterday over "severe crowding" on subway trains after last week's Fourth of July fireworks display on the Mall and said steps will be taken to improve transit service for next year's Independence Day celebration.

About 270,000 people converged on the subway system to get home after last week's concerts and fireworks. Metro officials said the crowd was the largest since the rail system opened nine years ago.

Many passengers faced considerable delays and much jostling. The subway system remained jammed until nearly 1 a.m., officials said.

The massive ridership resulted in the heaviest strain for the transit system on any Fourth of July since a widely criticized breakdown in Metrobus service on Independence Day during the bicentennial commemoration in 1976. The bicentennial mishaps were attributed to inadequate planning.

"We believe that we did a good job, an excellent job. There were no major incidents," said Metro General Manager Carmen E. Turner of last week's performance.

Among Fourth of July measures being considered for next year are shifts in subway service to relieve crowding at key stations.

Crowding was described as especially severe at Metro Center and L'Enfant Plaza, where passengers sought to transfer from one subway line to another. To ease crowding, officials said, they will consider steps to prevent riders from transferring until other passengers have boarded trains.

Officials said they may propose changes in the scheduling of Fourth of July events. Crowding would likely be reduced, officials said, if concerts ended considerably earlier than the fireworks. Some patrons would then leave the Mall before the fireworks began, they said.

Steps may be taken to prevent crowds from blocking buses on Independence Avenue, officials said. And Metro officials will consider prohibiting riders from carrying large beverage coolers on trains, raising Independence Day fares from 75 cents to $1 and issuing warnings about possible delays.

In other developments:

* Metro officials said new delays have occurred in plans to repair 76 buses manufactured by Neoplan U.S.A. Corp., a West German-affiliated company. The buses were removed from service in February because of cracks in their undercarriages. Metro officials cited objections to the company's repair work and expressed uncertainty about when the buses will be returned to service.

* A Metro committee recommended granting passes to firefighters and plainclothes police officers for free rides on subway trains and buses. The move would overturn a controversial action last year by the Metro board.

* The transit authority issued a report describing last year as Metro's "safest operational year." The report cited reductions in bus accidents.

* The Metro board approved changes in bus routes in Prince George's County. R15 service will be extended to east Greenbelt on July 22. Revisions will take effect Sept. 29 on C11, C14, P14, R12, T10, T14, T19, W11, W12, 84 and 85.