Legislatures are notorious for waiting until the eleventh hour to do their business, often jamming hundreds of votes into the last days of their annual sessions in a frenzy of decision-making that takes months to be sorted out. Courts, on the other hand, are supposed to be more orderly places, where decisions are made in a measured, scholarly fashion.

Not so. The U.S. Supreme Court, about this time each year, rushes through a countdown to the end of its nine-month session, cramming in all the work it failed to finish during the first 8 1/2 months. That crunch has rarely been as bad as this term.

During the next 15 work days, the court is expected to dispose of more than 70 cases, roughly 42 percent of the caseload it began accumulating last October. Most of those opinions could come in the final two weeks before the expected July 2 adjournment.

For court watchers, that means seven, eight, nine or more decisions in a single day, hundreds of pages of opinions, an avalanche of concurrences and dissents all at once, often covering the most controversial cases of the term.

Among the most watchable this year, for example, and still to come are the busing cases from Los Angeles and Seattle; the "kiddie porn" and school library censorship cases from New York; opinions on the constitutionality of the legislative veto, denial of free schooling to the children of illegal aliens; mental patients' right to refuse anti-psychotic drugs as well as the constitutionality of shackling the mentally retarded in institutions.

The court is also expected to announce rulings on the obligation of school systems to educate deaf children; on whether presidents can be sued for damages for violating the law (Richard M. Nixon is the defendant in the case), and whether lower level federal officials can be sued for damages for failing to carry out the law.

Decisions remain on which state gets to tax the estate of Howard Hughes, on corporations' state tax liability, on whether certain foreign owned firms in the U.S. may discriminate, and whether capital punishment may be imposed on someone who drove the getaway car but did not participate or plan a murder.

Several factors cause these deluges. Many of the late rulings were argued late in the term. Many are closely divided, requiring more time to reach agreement and more time to write dissents and concurrences. Some justices take a long time to write and some just write long.

In addition, say some knowledgeable in the court's inner workings, a longstanding tradition has broken down in recent years--that each justice respond promptly to draft opinions and dissents circulated by colleagues. Several justices now tend to hold onto a draft for inordinate periods of time--weeks or months--without responding.

That can hold up the whole process. In close cases, it can also mean an unnecessary delay before the court knows which view commands a majority and which will be a dissent. Then there is further delay while a draft is rewritten accordingly.

This year's deluge is worse than most in part because the court is considering more cases than usual--184 as opposed to 153 last year and 156 the year before.

No outsider can know with certainty whether the rush hurts the quality of the rulings. But many last-minute decisions are not noted for their coherence.

Last year one of the final decisions, involving billboard bans in California (Metromedia, Inc., vs. City of San Diego), was aptly described by one dissenter as a "Tower of Babel" because of its unintelligibility.

A second last-minute decision (Robbins vs. California), concerning police searches in automobiles, was overruled June 1, making it one of the shortest-lived precedents in recent Supreme Court memory.

The year before, a late ruling interpreting occupational safety and health laws (Industrial Union Department vs. American Petroleum Institute) was considered a monument of confusion by lawyers in that field. That and another final volley in 1979, the court's decision (Gannett Co., Inc. vs. DePasquale) allowing closed criminal pre-trial proceedings required major surgery by the court in the following term.

It is impossible to know, however, whether the rulings were messy because they were late or late because they were messy.

The court tries to finish most of its private voting and draft-circulating by June 1. Cases remaining may be held over until the following term. But they must then be reargued, at great additional expense to the parties involved.

Among the issues on the court's agenda for the next three weeks and the questions they aim to settle are:

* The constitutionality of voter initiatives blocking school busing to achieve integration in Seattle and Los Angeles. Do they impermissibly discriminate against the interests of minorities? The answer should help determine the future of busing in some areas as well as the reach of majority rule, in its most direct and explicit form, in any sensitive area involving basic minority rights.

* The vulnerability of U.S. presidents and their aides to damages suits stemming from violations of individual rights. Are they immune from damages? The case stems from a suit brought against Nixon by former Pentagon cost analyst A. Ernest Fitzgerald, alleging that he lost his job for blowing the whistle on cost overruns.

* The power of the House of Representatives or the U.S. Senate to exercise a "legislative veto" over regulatory or executive branch decisions. The case involves a legislative veto provision in the immigration laws, but could determine whether Congress can block Federal Trade Commission regulations, for example, requiring disclosure of flaws in used cars as it did May 25.

* How much individual freedom the Constitution guarantees to involuntarily committed mental patients and the institutionalized retarded? Two cases scheduled for decision concern the right of mental patients to refuse anti-psychotic drugs and the right of the retarded to be free of physical restraints. The cases involve the power of the federal courts to intervene in the management of state homes and hospitals.

* Whether the nation's new system of bankruptcy courts, established by Congress in 1978 and getting more use now than ever, violates the Constitution. A lower court struck down the law creating the system on grounds it gave bankruptcy judges many powers of U.S. district judges, but denied them the life terms and salary protections the Constitution requires to insulate judges from political pressures.

* The constitutionality of sex-segregated state schools, specifically an all-woman nursing school in Mississippi.

* Whether school libraries are protected by First Amendment free speech guarantees from censorship by school boards. This case, from Island Trees, N.Y., could determine the future of the "book banning" campaigns orchestrated by groups that don't approve of what their children are allowed to read.

* Whether a state may ban dissemination of pictures, even when not legally adjudged obscene, of children engaged in sexual acts. The New York Court of Appeals struck down that state's "kiddie-porn" law on the grounds that it could be applied to non-obscene pictures, such as art, protected by the First Amendment.