Metro's transit system has survived the jarring impact that accompanied the opening of the subway's Blue Line and the redrawing of the bus network a year ago to post a solid increase in ridership in the year that ended June 30.

Metro's quarterty report on ridership, released yesterday, shows that people made an average of 22,000 more trips a day on Metro's combined bus and subway system in fiscal 1978 than they did in fiscal 1977.

That average increase - 5 percent - was achieved despite a heavy drop in ridership that accompanied unreliable train service and a dramatically revised bus system that characterized public transit here last July, August and September.

As Metro's reliability has increased (98 percent of all scheduled subway trips are now completed), so has its ridership.

Proof of that comes in a comparison of Metro's ridership from June 1977 to June 1978. According to the report, 70,000 more transit trips daily were made this June than last, a 17 per cent increase.

Metro General Manager Theodore C. Lutz could not hide his enthusiasm over these figures in his cover memorandum to the report. "The initiation of the (Silver Spring subway extension) is one of the factors in this increase," Lutz said, "but even at these new stations, ridership is exceeding our original projections."

The report does not include two recent events that undoubtedly wil harm ridership at least for awhile: a fare increase that went into effect July 1 and a seven-day transit strike in the middle of July. The next quarterly report should give some indication of the long-term impacts, if any, of those two events.

Transit use has been increasing steadily over the past four years as Metro has gone from an all-bus system in fiscal 1975 to a combined bus-and-rail network now. Total transit trips on an annual daily average have increased during that period from 375,525 a day to 435,723 a day - or 15.7 percent. When downtown minibus and school trips are included, Metro is now providing well over a half-million trips a day.

Although the subway is attracting an increasing number of people, buses continue to be the backbone of the Metro system in terms of trips generated. That ratio is continually shifting in the direction of the subway, however, as more of the subway system is opened and as more bus routes are tailored to neighborhood service.

On May 17, when Metro officials took a detailed count as part of the ridership survey, 184,288 rail trips were recorded. Two trips out of five entailed the use of both the bus and the subway; the other three trips out of five were subway only.

Critics of the subway have charged that Metro is really just transferring people from one kind of transit system to another. But there is growing evidence that the subway is carrying people whom the bus would never get.

Part of that comes from the fact that all the Metro stations that have parking losts attached now have full parking lots.

Other evidence includes steadily increasing midday ridership on the subway alone, and not just in the downtown area. "Ridership increases have occurred in virtually every half-hour increment throughout the day since the time of the last passenger count," the report says.

The report also shows that transit riders in Washington are not stupid. Metro's fare structure makes it impossible to transfer from bus to subway without paying two full fares. However, it is possible to transfer from subway to bus.

Therefore, contrary to every known law of transit patterns, Metro's subway ridership is higher in the evening rush than in the morning.