Call it monkey business, Senate-style.

The "continuing resolution" that Congress must pass by midnight Thursday to carry the government through the first few months of the new fiscal year is supposed to cover just bare essentials, with all the extra goodies deferred until regular appropriations bills are passed.

But each senator has his own definition of essential, which in the case of Sen. Harrison H. Schmitt (R-N.M.) is broad enough to include $500,000 for a "chimpanzee colony" (pop. 60) at New Mexico State University.

Schmitt is normally as economy-minded as the next Republican. But he has a tough race for reelection on Nov. 2 and, as chairman of the Senate Appropriations subcommittee on labor, health, human services and education, is in a powerful position to say what gets spent in many major areas of discretionary domestic spending.

So the $500,000, earmarked as part of $3.9 billion for the National Institutes of Health, is included in the omnibus stopgap funding bill for the government on which the Senate is expected to complete work today.

In general, the measure continues existing funding levels or modifies them to reflect appropriations bills that have passed one house or the other. In most cases, it maintains existing spending restrictions ranging from the pay ceiling on high-level federal workers to a ban on oil and gas leasing in wilderness areas.

While there are also some further detailed restrictions, such as proposed curbs on activities by Legal Services Corporation lawyers and a proposed ban on regulation of doctors, lawyers and other professionals by the Federal Trade Commission, most of the bill is general in nature, mainly referring to legislation that has been passed or is making its way through Congress on other tracks.

But tucked into the committee's report is this language: "$500,000 shall be provided in fiscal 1983 to provide support to the New Mexico State University chimpanzee colony to improve facilities there to maintain a nucleus of about 60 animals for use in biomedical research and to produce additional animals."

"This is an essential facility to breed chimpanzees for research," Schmitt explained, " . . . and it's running short of money," especially for "rehabilitating" the chimps between experiments.

As to why New Mexico was favored when some other senators' "essential" projects were put off, Schmitt smiled and responded:

"We try to accommodate what we can, but, of course, when you're chairman of a subcommittee you tend to look at the problems you know best. We try to accommodate other members of the appropriations committee too, when we can. That's one of the advantages of being on the Appropriations Committee. It's the way the Congress works."

Another way in which it works is that what the House giveth, the Senate often taketh away.

In the House, Rep. Silvio O. Conte (R-Mass.), ranking Republican on the House Appropriations Committee, figures that money for Massachusetts falls in the essential category. So he included in the House version of the bill language mandating continuation of a government contract with Boston University for regional health delivery projects in West Africa. The Senate committee, however, without a Massachusetts booster in its ranks, dropped Conte's language.

But the Senate's deference to Schmitt did not end with monkeys. Also included in the Senate version of the bill is a stipulation that $200 million for purchase of strategic materials be devoted to buying copper. With unemployment running high in copper-smelting regions of New Mexico, Schmitt tried but failed to get a somewhat different boon for the copper industry in another appropriations bill earlier this year.