Recently in Colorado, the state's senior senator was taken to task by a local political wag at a banquet where poking fun was the order of the evening.

"Just six years ago," said the wag, "a man was running for the Senate, and the people of Colorado were saying, 'Who is he? What does he stand for?' And now, a brief six years later, Floyd Haskell is running for reelection, and people are saying, 'Who is he? What does he stand for?'"

The line got a good laugh from the 600 Democrats in the hall, probably because it states so clearly Haskell's predicment. On Capitol Hill Floyd Haskell is known as a serious reasonably hard-working senator who occasionally has exposed his neck for controversial causes.

He has a reputation for expertise on taxation, many energy matters and wilderness issues. But in Colorado, according to his own staff and independent observers in the state, Haskell's image is still vague - dangerously vague for a senator running for reelection.

Of course, Haskell's image was also less that precise when he deposed Sen. Gordan Allott in 1972, so neither he nor his associates despair of his chances.

Haskell's problem is a familiar one for incumbents, particularly incumbents who lock seniority: how does one senator who is not a committee chairman, who is not memorialized by some famous piece of legislation, who has not conducted nationally televised investigative hearings, convince his contituents they need his services enough to reelect him?

"They don't" 'know what you do," Haskell said of his contituents during an interview. "They don't know about your committee work, your legislation." At the same time, he noted, potential opponents are offered an inviting target when they take on an incumbent: his voting record.

Colorado is a politically volatile state where close races are typical. Haskell's attempt to win reelection will succeed or fail on the basis of a few thousand votes, in all likelihood. Haskell asknowledges he might have alienated people whose votes he could need.

One bloc he admitted alienating was the "right-to-life" camp, the militant anti-abortionists. When asked about them, Haskell said: "Well my history is so consistent (in favor of abortion in many circumstances), and furthermore I have three daughters in their 20s, and if I should change my position on abortion I might as well read myself out of the family. There's no way I'm going to change."

That seemed to be that. But suddenly, a few minutes later in the same conversation, Haskell returned to the abortion problem without being asked about it again: "Abortion," he said, sounding as though he had been thinking about this all along, "It all depends on how strongly people feel, how big the right-to lifers are in Colorado at that (election) time."

And then the voice of the politician who isn't sure:

"I don't honestly think - we have a fair Catholic sentiment, but the Catholics in our state, at least the ones I've run into, are pretty reasonable folks."

Haskell and his associates have learned one of the sadder political truths: the people you anger don't forget, but the people you try to help may never know you tried.

And Haskell has angered some important interest groups - most of the oil and gas industry, for example, Haskell took a stronger position against deregulation of natural gas prices than any other Colorado congressman, including Sen. Gary Hart and House liberals like Patricia Schroeder and Timothy E. Wirth.

He has favored barring oil companies from owning other kinds of energy sources, and he's taken what he calls "pro-competition" positions on other oil-related issues in the Senate Energy Committee.

Earlier in his term, as an active mamber of the public lands subcommittee of what was then the Interior Committee, Haskell angered some Colorado interests by pressing for larger federally protected wilderness areas than they wanted.

Haskell's other major committee assignment has been to the Finance Committee, where he and Sen. William D. Hathaway (D-Maine) have been lonely advocates of radical rax overhauls. Few of Haskell's initiatives there have made any headway, but he did manage to insert one change in the 1976 tax law that had a substantial impact on the real estate industry to contribute heavily to his opponent this year.

In all of these cases and others, Haskell angered a special interest allegedly to benefit a broader public purpose, but both his aides and his political friends despair at Haskell's inability to make this point forcefully in public. "He just won't grandstand," as one aide put it. "People don't know what he's done."

"He's not a politician," said Gov. Richard Lamm of Colorado, another liberal Democrat who faces a tough reelection campaign this year.

Even if he was the best grandstander in Washington, though, Haskell's record as a senator is not one the crowd in the bleachers could readily grasp or appreciate. Apparently one of his most significant accomplishments, for example, was to rewrite the basic legislation governing the Bureau of Land Management.

In the Finance Committee, Haskell's role has been that of the gadfly, persistently pushing for revisions no more than a handfull of colleagues would support. When the 1976 tax revision was on the floor of the SenateM Haskell offered a series of "kamikaze amendments," as one aide described them, most of which got no more than 10 votes.

Samantha Senger Sanchez, a tax expert who worked for Haskell on tax overhaul for several years, aid a long series of 17-to-2 defeats in the Finance Committee makes "you realize that your effectiveness is about zero." In the end, she said - and others on Haskell's staff confirmed - the senator's interest in tax overhaul waned.

"He tends to be too much of a gentleman to take on dirty fights," Sanchez said. "He would just state his case and say all right, let's vote. But Russell Long (chairman of Finance) is not the sort of person that functions on the merits" of issues.

In sum, Haskell's record on taxes is that of a senator who fought persistently for tax "reforms" intended to make wealthier people pay more tax. Theoretically, at least, this might be a politically advantageous record, but Haskell has two problems: very few people know what he tried to do, and he succeeded in doing almost nothing.

Another of Haskell's substantial accomplishments was in the area of small business. He sponsored and Congress eventually enacted a tax credit to encourage small businesses to hire new employees. This was a substantial boon to many small businessmen, and Haskell is much praised by the representatives of organized small business groups.

"But a lot of people eligible for the credit don't even know it exists," one of the senator's aides said.

The Treasury Department disapproved of the credit, so it has not advertised it widely, this aide said. And Haskell's role is not exactly on the lips of every small businessman in the land.

A younger or more ambitious senator - a man who was more of a politician - might have looked for ways to make bigger splash in the Senate, but not Haskell. Indeed, if one follows him for a few days, it becomes obvious that the details of federal policies that affect small business for example, really interest Floyd Haskell. He'll go on talking about them for hours.

But Haskell is not blind to the needs of an election year, and he has been trying to make some political use of his incumbency. Last month for example, he introduced a complex farm bill intended to meet the concerns of American farmers by raisin price supports for some crops in specified circumstances.

Haskell acknowledges that this new approach to price supports is not going to be adipted at once, but he wanted to get the idea into the public debate. The American Agriculture movement, which has led this year's national wave of demonstrations for new farm legislation, was founded in Colorado and enjoys strong support there.

The senator also joined severeal colleagues in proposing reconsideration and reduction of last year's sharp increases in Social Security taxes. The gesture was widely covered in the Colorado press.

Last month Haskell held two public hearings in his state on the relationship between limited water supplies and various ambitious plans for the development of new energy sources in the West.

During the year he plans other hearings here and in Colorado on energy-related matters in his capacity as chairman of the production and supply subcommittee of the Energy Committee.

If any of Haskell's senatorial roles will play well in his campaign, this subcommittee charimanship should be it. Colorado has vast oil-shade resources whose development could transform the state's economy. Haskell has been pressing for federally financed demionstration projects to test the economic feasibility of shale exploitation, as well as other alternative energy sources, including solar.

Asked why he wants to be reelected to the Senate, Haskell says "unfinished business" in the energy field is the principal reason. "We must have a true test of alternate technologies on a commercial basis," he says.

But in his wilderness concerns and in other votes, Haskell also has tried to establish environmentalist credentials. He emphasized the environment in his first Senate campaign managers hope to sell him as a concerned, common-sense senator whose expertise and committee assignments make him a valuable asset to Coloradoans.

His simultaneous concerns for cautious development of new energy resources, protection of water supplies and the environment make him "the right man for Colorado," as one campaign aide put it.

But Haskell and his colleagues still must package the senator and his complex record in a way that will appeal to the voters.

Jill Buckley, a political consultant and partner in the firm of Rothstein-Buckley, which is planning the Haskell campaign, said the other day, "We're still grappling with how best to position him."