Land of Goshen, how that clock runs.

It wasn't all that long ago that Mo Udall was what they called a reformist young Turk connonading around the autocratic House of Representatives.

And only four years ago. Udall was running for the Democratic presidential nomination, running a far more respectable race in the primaries than his 320 delegate votes would imply.

Now, tonight, you'll have Udall on the tube, in the role of the paternal, sage unifier, a Kennedy supporter picked by Jimmy Carter to keynote the Democratic National Convention.

It remains to be seen how much unifying Rep. Morris K. Udall (D-Ariz.) can do among those contentious factions, but his speech ought to be a humdinger.

In the House, where talent always rises above partisanship, Udall is regarded by Republicans and Democrats alike as one of the chamber's best, most thoughful and wittiest speakers.

He got that way, in part, because he is an obsessive collector of political humor, neatly kept for four loose-leaf notebooks that keep growing with the appropriate tale for the appropriate moment.

Apropos of which, an old story with a contemporary application: In 1948, when Harry Truman's presidency seemed to be going down the tubes, Alben Barkley of Kentucky was the Democratic keynote speaker.

Udall's notebook has a Barkley yarn about a Kentucky moonshiner who, at gunpoint, forced an accomplice to try his white lightning, then handed the gun over so he could be forced to take a nip, too.

The point this illustrates, Udall mused the other day, is that "we Democrats have got to hold the gun on each other for the next 100 days, or we'll have this Reagan disaster upon us."

That, or something like it, is likely to be a theme in his keynote, but that is getting ahead of this story, which is really about whatever happended to Mo Udall.

After the 1976 presidential race, Udall went back to doing what he does best, representing the Tucson area in the House and riding herd on environmental matters as chairman of the Interior Committee.

He became chairman in 1977, just at a time when the environmental army was getting backed down on one issue after another. That made it tough on Udall, an environmentalist politician, and on his unbudging friends in the movement.

Because he is a student of the possible, Udall is forever staking out middle-ground positions in his committee, seeking the compromise and accommodation that will keep an issue on track.

Republicans and conservative Democrats on the committee recognize and appreciate Udall's style, but it exasperates some environmentalists.

"We're having some hideous fights with Mo on issues like nuclear regulation, reclamation law, the coal-supply pipeline," an environmental lobbyist said on the eve of a recent fund-raiser she and friends were holding for Udall.

For all the fights, however, Udall is still their friend and they recognize it. He is caught up this year in a bitter reelection battle against a conservative GOP candidate who is getting massive financial aid from all over the country.

"It's going to be a rough year," Udall said. "But if I go down, I will probably go down in good company."

He seems as serene about that as he was after losing the nomination in 1976. Looking back, he observes: "I'm proud I made it that far in the big time . . . and I'm pretty proud of what we've done in the Interior Committee the last four years."

One of the things he did at the committee was put into practice the reforms of scheduling and openness he had advocated for so long as a House insurgent in the 1960s and early 1970s.

"If a subcomittee sends up a bill I don't like, I will schedule it anyway with the full committee," he said. "It didn't used to be that way around here. The impact of the revolution in the House has been pretty substantial."

One of the ranking Republicans on the committee, Rep. Robert J. Lagomarsino of California, commented on Udall's style.

"Disregarding our differences on the issues, he is always fair, competent and able." Lagomarsino said. "On some issues he's not as strident and he is perhaps more willing than others to compromise, trying to persuade them to come to the middle."

But there are times when Udall draws a line in the political sand and will compromise no more.

For years, before and after he was chairman, he caught holy Ned from environmentalists for compromising on a strip-mine control bill. Carter signed the bill into law, saying he wished it were tougher.

But when the Senate last year moved to gut the law, Udall scuttled the Senate amendments in his committee and stopped them dead.

His insistence that a strong Alaska lands bill be enacted has won him some enmity on the committee and in Alaska, whose delegates to the convention have threatened to walk out during his keynote speech.

But it has earned him undying praise from environmentalists.

"No question about it," said the Sierra Club's Sandy Speoliscy. "He's been outstanding on the Alaska issue. He sets standards we wish would be set by the rest."

Ironically, Udall is sometimes victimized as chairman by the openness and fairness of procedure that he championed for so long. He gives an inch, then his opponents take two more.

"Mo came here in 1961 [succeeding his brother, Stewart, who became secretary of interior] and led the reforms on seniority and that has affected his control," one of his aides said. "He is so kind and so magnanimous that people take advantage of it."

Those campaigns included a 1969 challenge to speaker John McCormack (D-Mass.) and a run for majority leader in 1971, leadership of the move to oust Adam Clayton Powell (D-N.Y.) for abuse of a chairmanship in 1967, strong advocacy of broader financial disclosure, and revision of the seniority system, campaign-spending and contribution limits.

Now 58, a little grayer and a little heavier, the former professional basketball player may not be quite as quick in going to his left. But Udall doesn't see that much change in himself.

"Oh, 1976 took a lot our of me. After the election, I broke both arms, had an appendectomy and viral penumonia," he said. "But I still think of myself as a young Turk going against the old senior members who won't bend."