It is never exactly a month of Sundays on Capitol Hill, but in May it comes close. For these are the days of the high school senior onslaught.

Ah, the freshness of it all. As they obtain their gallery passes, the seniors actually say "please" and "thank you." As they wander the halls, the seniors actually refrain from smacking their gum. And every time they pass a Teddy Kennedy or an Ed Muskie, they ooh right on cue.

But reverence is apparently for the young. Last Monday, deep in the heart of the Rayburn Building, a lady about 60 inches high and at least that many years old approached a congressman. She had no-nonsense written all over her.

"Listen, sonny," she began. And fellow Americans, that congressman sure did.

If May has always been high school month on the Hill, it israpidly becoming senior citizen month, too. For the sixth consecutive year, the Hill has just finished hosting a one-week "senior interns" program. This year's was the biggest ever, and quite probably the msot fruitful.

The purpose of the internship is for the elderly to see what happens to programs affecting them on Capitol Hill. But it also allows the Hill establishment to hear from the interns first hand.

During their Washington week, interns technically serve as congressional staffers. They research, and discourse on, such subjects as Social Security, transportation, housing and Medicare. They must be at least 60, and they must be people who work in senior citizen programs back home.

The fact tht they are also voters, and sway other voters, is not mentioned out loud by congressional sponsors. But it is hardly an accident that 107 senators and congressmen nominated 146 interns this year. "The word is spreading," noted Donna Norton, executive assistant to Rep. Elwood Hillis (R-Ind.), who helped originate the program.

One place it spread was to the hamlet of Cabbage Corner, Del. That is the turf of Jennie Kennedy, a recent arrival among the ranks of senior citizens (she is 61), but a sparkplug in five senior citizen programs in Sussex County. When Sen. William V. Roth Jr. invited her to serve as an intern, she hesitated for about one instant.

Kennedy's major interest is the lower-income elderly, who, as she says, "include most of the people I work with." The problem is that, if they are too poor, they cannot afford the private nursing homes near Cabbage Corner.

The state operates a home in Smyrna, but that is 40 miles away - and about a world away in terms of what Cabbage Cornerities are used to. "They'd rather keep their dignity and stay at home," Kennedy said.

Kennedy did not win a fabulous federal grant for Cabbage Corner during her week in Washington, and she did not expect to.

"But I have learned a great deal," Kennedy said. "I've learned how these things work, how the money goes from Washington to the state and then to us. I've gotten lots of good answers. Now it's up to the individuals."

Kennedy's fellow Delaware delegate, Roy Rudy, 82, has never had difficulty being an individual. As a young man, he sold women's ready-to-wear clothing door-to-door in Alaska. He once spent six years touring the country in a camper.

Now retired in Newark, Del., Rudy had never thought much about the political process before his internship. After last week, he was thinking about it a lot.

"Now that I've been here, I can see that every letter that comes in gets evaluated and answered," Rudy said. "There's always a solution to every problem. They're looking for solutions here."

Rudy granted that that last statement might produce howls of laughter back in Newark.

Sure, some people are cynical about Washington," he said. "But the senior citizens don't have time for that. You can only do so much."

When you do anything on Capitol Hill, standard procedure says to be sure that your name gets attached to it. But Roth denied that that was his motive when he took on the task of organizing the intern program on the Senate side six years ago.

"Results are really the point," Roth said. "They don't care who you are, or whether you've got a tough primary fight ahead of you. And that's the point, really."

Another inescapable point is who pays for the intern program. At present, the taxpayers do, to the tune of $300 per intern.

The interns make little if any profit, since their expenses come out of that sum. But inflation may turn $300 into too few dollars one year soon. Anticipating that, Roth tried to increase the stipend to $350 per intern early this month, but his bill was defeated by the Senate.

Still, the program is in no danger. Some interns had their way paid this year by senior citizens who took up collections over the winter. A few even paid their own way.

And many more would if they had to, believes Jeanette Nadler, of Lynn, Mass.

"Our generation has a lot of pride," she said. "We're used to being self-sufficient. I think this program is great because anything that comes from Washington is an unexpected bonus."

Now, if could work on that reverence just a little . . .