Scientists are supposed to be different, so nobody gave Dr. David P. Rall's attire a second look when he strolled into the little hearing room.

It was a chilly day back in February. Rall was on Capitol Hill with other officials from the National Institutes of Health to explain how they would spend federal money in fiscal 1981.

On a day like that there's no monkey business. They put on conservative suits and purposeful faces, rehearse their statements and try to leave a good impression with the members of Congress.

Rall, director of the National Institute of Environmental Health Sciences, had on a jaunty sports jacket. But it was the khaki web belt around his waist that caught the eye. In neat black letters, it said:

Support Environmental Health With Dollars and Positions.

Unorthodox, yes, but to the point. "I wear it once a year," Rall told a bystander. No further explanation was needed, because Rall's belt told the story.

Once a year, he and the NIH directors trundle themselves up to Capitol Hill to go through the ritual of testifying before the House and Senate Appropriations committees to justify their existence.

Now jump forward to August. The House Appropriations subcommittee for labor, health, education and welfare rewarded Rall's institute with an increase: $3.5 million more than President Carter had requested.

Within days, without even a flicker of inquiry, the full Appropriations Committee and the House had given their stamps of approval and sent it on to the Senate for action.

That's the way it happens most years. It had happened again this year by the time the House finished its NIH appropriation. The House gave NIH $3.6 billion for research work, some $126 million more than Carter requested. That is 5.5 percent more than NIH got in fiscal 1980; 13.5 percent more than in 1979.

So far, the script closely tracks the historical pattern. But this has been a year like no other and here, near mid-October, Congress still has not completed work on what it began in January.

Ordinarily, it works this way: the president sends his budget to Congress in January. The House subcommittees, where the constitutional process must start, quickly begin hearings. They hear government and outside witnesses, decide how to allocate the money and send their bills to the Appropriations Committee.

Another leveling goes on there, the bills move on the House floor, items are changed, and final action propels the measures to the Senate. There the process is repeated. A final version of each spending bill is worked out in a conference and it goes to the White House for presidential signing or veto.

This year Carter sent his budget to the Hill in January. Then the economy took a nose dive and he decided to tighten federal spending. Cuts were worked out, and a new budget went to Congress in April, delaying the ordinary process about three months.

Congress, meanwhile, was caught in the complications of the congressional budget process it set up in 1974 to get a better handle on spending.

After a week of consultations with the administration, the House and Senate Budget committees worked out their own versions of a balanced budget for fiscal 1981. All the versions varied, leading to more debate and negotiating.

A final budget resolution, establishing the spending targets for federal programs, was not ready until mid-June. House Appropriations subcommittees, ordinarily done by then, could not move until the resolution was ready.

But by then the process was horribly off schedule. When Congress recessed earlier this month, the Senate Appropriations subcommittee still had not started marking up its version of the NIH budget for a fiscal year that already had begun.

Under that kind of gun, and with federal agencies faced with running out of money (they can't spend it if it's not appropriated), Congress passed a resolution to assure continuity.

It means that until Dec. 15, when the continuing resolution will expire, NIH must spend at the levels established by Congress for FY 1980. It can start no new programs nor can it change old ones.

When the Senate returns after the Nov. 4 election, its health subcommittee will try to pick up the thread and crank out an NIH appropriation for FY 1981.

As of now, according to committee sources, there are no major disputes looming over the House-passed version. One of the features of the House bill, in fact, may thrill the Senate. Against the recommendations of Carter and Dr. Donald Fredrickson, the NIH director, the House added $35 million to expand the institutes' research-training programs.

Carter, pleading fiscal restraint and reacting to his Office of Management and Budget, which historically has not liked training grants, had recommended sharp cuts in that area. The Senate last year had urged increases in training.

There is a difference in approach, however. Senate eyebrows may arch when they read the official committee report accompanying the House bill. Much of it was written by NIH.

That, it turns out, is a long-followed practice in the House. Theoretically, Congress and the executive branch are separate and independent. But for years, the House appropriators have allowed the agencies to provide "suggested" language for the reports, which explain the bills and direct the bureaucrats.

If it sounds as if the bureaucratic tail wags the congressional dog, just remember Dave Rall's khaki belt. The House followed his instructions to the letter.