You worked late at your office. And now you're running to catch a subway train to get home. As you dash down an escalator that's stopped moving and struggle with a farecard machine that's on the blink, a knot forms in the pit of your stomach.

Is that a train rumbling below? If you race for the platform, will the train pull out just as you reach it? How long will you have to wait for another--5 minutes, 10, or more? If you stick around, will the next train get you in fast enough to catch your bus? Or should you phone home to plead for a ride?

Believe it or not, Metro has answers to some of the questions that perplex subway patrons. Hidden in the transit authority's computers are minute-by-minute timetables. They show when each train is scheduled to run on the Blue, Orange, Red and Yellow lines. And, Metro officials say, most of the trains run on time.

In June, for example, the transit authority's records indicated that 99.5 percent of the trains were on schedule. In other words, delays were reported fewer than five times a day. Some minor holdups may not show up in Metro's records, officials note. Nevertheless, they say, it appears likely that the subway system stays on schedule at least 95 percent of the time.

If you worked late and missed the 8:06 p.m. train at L'Enfant Plaza on the Yellow Line to Northern Virginia, the next subway would arrive at 8:18 p.m. It would get you to the Pentagon at 8:23 p.m. and to National Airport at 8:29 p.m.

If your lunch plans require a midday trip from Metro Center to Rosslyn on the Blue and Orange lines, a 12:17 p.m. train would get you in at 12:24 p.m. If you went to a Saturday night movie near Dupont Circle and wanted to get back to Silver Spring on the Red Line, you could take a subway at 11:12 p.m., 11:27 p.m. or 11:45 p.m. The trip would take 22 minutes.

You've never seen a subway timetable? Of course not. Metro doesn't publish one. The transit agency prints and distributes schedules for its bus routes, but not for its subway system. Indeed, Metro is virtually the only major transit authority in the United States that has not taken steps to publish a rail timetable.

Why? "It's a philosophical question," said Robert A. Pickett, Metro's assistant planning director. "When you're running fairly frequent service on a regular basis, then the need for a schedule isn't there."

Then why do so many other transit authorities publish rail schedules? "Maybe all the other systems ought to ask themselves, 'Why do we do it?' " replied Metro marketing director John E. Warrington. "On my priority list, that would be way down bottom."

Metro officials agreed, nevertheless, to make public its rail schedule in response to a request from The Washington Post. (Metro's rail timetable for the Red and Yellow lines appears in today's Weekly editions. Schedules for the Blue and Orange lines will appear next week.) Carmen E. Turner, Metro's newly appointed general manager, has recently started looking into whether the transit authority should publish a rail timetable, according to a Metro spokesman.

In Atlanta, Boston, Cleveland and Philadelphia, timetables are available free to rail patrons, according to transit officials there. They are published by PATCO (the Port Authority Transit Corp.), which links Philadelphia with southern New Jersey, and by PATH (the Port Authority Trans-Hudson Corp.), which connects New York City with Newark, Jersey City and Hoboken.

In San Francisco, BART (the Bay Area Rapid Transit District) has long published timetables for evening and weekend service, and it recently printed its first weekday timetable. "People have been waiting for a schedule," said BART spokesman Sy Mouber. "If they have something in their pocket, they feel more secure. It was for passenger convenience."

In New York City, elaborate plans are under way to install "Guide-A-Ride" signs, including computer-printed timetables, in more than 500 subway stations and to publish free pocket schedules of subway service later this year. The Chicago Transit Authority appears to be the only major exception, besides Metro. A spokesman said the CTA publishes schedules for two of its rail lines, but not for its other five.

A glance at Metro's timetable may help clear up some day-to-day confusion. When, for example, does rush-hour subway service start, or end?

You may think, quite reasonably, that rush hours occur during two 3 1/2-hour periods every weekday--from 6 to 9:30 a.m. and, again, from 3 to 6:30 p.m. Those are, indeed, the hours when rush-hour fares are in effect. (Rush-hour fares include a surcharge of 14.5 cents a mile for trips longer than 3 miles. The surcharge is added to Metro's basic 75-cent subway fare.)

But if you imagine that rush-hour subway service starts at the same time that rush-hour fares go into effect, guess again. Rush-hour service, which is twice as frequent as most midday and evening service, may begin later or end earlier than the times at which rush-hour fares are charged.

On the Red Line, for example, trains are scheduled to leave the Van Ness station every 10 minutes until 7:13 a.m., when they start running every 5 minutes. In the opposite direction, Red Line trains depart at 5-minute intervals starting at 6:39 a.m.; their frequency is reduced slightly after 8:44 a.m., and they switch back to 10-minute intervals at 8:59 a.m.

You may have heard, as is frequently said by transit officials, that you should never have to wait more than 10 or 12 minutes for a train, if they are running on time. For the most part, such claims are borne out by Metro's timetable--but not during late evening hours. The timetable shows that you may have to wait 15 minutes, or a bit longer, after 10 p.m. or so.

Metro's current timetable, like those kept by most other transit authorities, includes some subway stations but omits others.

On the Red Line, for example, the timetable shows when trains are scheduled to reach Metro Center and Union Station. It omits two intermediate stops, Gallery Place and Judiciary Square. The ride from Metro Center to Union Station takes just four minutes, however. So it is fairly easy to gauge how soon a train should reach the intervening stops.

While Metro does not publish a rail timetable, it does provide some information about train schedules for its patrons. Signs displayed at subway stations indicate, for example, when the last train will depart each evening.

In addition, a rider may find out when trains are scheduled to reach specific stations by calling Metro's information number, 637-2437. Employes who answer questions at that number do not volunteer departure times, but they will look them up if a caller specifically asks to check Metro's rail schedule.