Busloads of young people from up and down the East Coast gathered at the Department of Labor in a midday downpour yesterday to protest President Reagan's proposed subminimum wage for teen-agers.

"The subminimum wages will lead to subminimum jobs . . . resulting in subminimum lives," Bill Morton, an organizer of the protest, told an audience of about 600 youngsters, including several busloads of District students. "What we want is an opportunity . . . for a better future," he said to cheers.

Morton, coordinator of the sponsoring Coalition for Youth, Jobs and Fair Wages, said the gathering was to "send a message to the president, to Congress, and especially the president's new secretary of labor, William Brock . . . that the subminimum wage is a subminimum idea."

Next week, the Senate Labor and Human Resources Committee will begin hearings on a Reagan administration proposal to allow employers to pay persons aged 16 to 19 a subminimum wage of $2.50 an hour, about 75 percent of the current $3.35 hourly minimum. For four years the administration has favored such a change, organized labor has denounced it and Congress has delayed action on it.

Supporters of the proposal, including D.C. Mayor Marion Barry, say a subminimum wage would encourage employers to hire jobless youngsters. Opponents argue that employers would favor teen-agers over adults, because hiring them would be cheaper.

In a partial turnaround for the administration, Brock has said he has "reservations" about the subminimum wage and that he would approve it only on a trial basis. The current proposal would allow the reduced wages only in the summer months of 1986 and 1987, from May 1 to Sept. 30.

Morton, who said he formed the coalition of 40 national youth groups about six weeks ago, planned to deliver a letter to Brock after yesterday's protest, requesting that the secretary meet with members of the coalition. Between speeches by students, some of whom had boarded buses at midnight to journey to the capital, protestors chanted: "We deserve a break today! Equal work for equal pay!"

"The fact is fast food and amusement park industries have pushed for a subminimum wage for years," said Morton. "Imagine that -- fast food makes $4 billion in three years while we struggle along for $2.50 an hour. Does that sound fair?"

Students from all over seemed to bring a consistent resolve to oppose the measure. "I'm here to say everyone should have equal pay for equal work," said Anna Batts, a 21-year-old Philadelphian standing in the crowd. "I make $7.50 an hour as a switchboard operator. A lot of teen-agers have to pay rent and utilities just like I do. They should make the same money I make."

Kathleen Murphy, a 17-year-old senior at T.C. Williams High School in Alexandria, delivered to the coalition a petition, which 200 students had signed.

"It [the pay proposal] discriminates against young workers," Murphy said, "and I'm convinced the wages would displace older workers."