President Carter endorsed legislation yesterday that would end federal criminal penalties for the possession of one ounce or less of marijuana.

But even before his drug abuse message to Congress was made public, the President's White House adviser on drug abuse, Dr. Peter Bourne, told reporters that federal decriminalization of marijuana is "not that important in the big picture" and that its significance in the message "is more symbolic than real."

The bulk of the message, when Carter introduced in a personal appearance in the White House press briefing from dealt with a series of studies and directives aimed at expanding and strengthening federal drug abuse efforts and placing coordination of those efforts under the White House.

The President did not propose administration legislation to decriminalize marijuana, nor did he urge the states to end their own criminal penalties for possession of a small amount of the drug - generally defined as one ounce of less. Instead, he said he would leave it up to the states to enact or repeal their own laws and he supported legislation pending in Congress that would impose federal civil penalties rather than criminal penalties for the possession of an ounce or less of marijuana.

Federal law now has a penalty of one year in prison, a $5,000 fine or both for possession of marijuana. There is no federal civil penalty for possession.

There are currently two Capitol Hill dealing with the subject. One would simply end the criminal penalty of a $100 fine for possession. In effect, Carter endorsed the latter measure, whose chief sponsors are Sens. Jacob K. Javits (R-N.Y) and Alan Cranston (D-Calif.).

The President, whose three sons have acknowledged experimenting with marijuana, primised during his campaign last year to seek to desriminalize marijuana. In doing so yesterday, however, he appeared to take the most cautious approach open to him - endorsing pending legislation rather than proposing his own and stopping short of urgin the states, which prosecute almost all marijuana offenders, to follow suit.

According to the National Organization for the Reform of Marijuana Laws, a Washington-based lobbying group, in 1975 there were 416,000 arrests under state laws for possession of marijuana. Of these, 93 per cent were for possession of a small amount - generally one ounce or less.

That same year, there were 4,000 arrests under the federal law Carter seeks to change, almost all of them involving traffickers who possessed more than one ounce, according to the organization.

The White House estimated that 45 million Americans have experimented with marijuana and that 11 million use the drug regularly.

In a telephone interview, Bourne said that while the President did not urge the states to decriminalize possession of marijuana, his endorsement of the pending federal legislation "signals certain message."

Some proposals in the message may draw criticism from civil libertarians. Carter, for example, ordered a Justice Department study of the possibility of denying release from jail before trial of persons charged with major drug trafficking offenses. he also ordered studies on the possibility of revoking the passports and freezing the financial assets of known drug traffickers, and of easing restrictions on government access to personal financial data of known drug dealers.

The President also ordered studies on the use of barbiturates, including the prescribing practices of physicians, an audit of drug manufacturing frims and the use of sedative hypnotic drugs that are particularly subject to abuse.

Bourne said he considered the President's emphasis on international cooperation to eliminate the sources of such drugs as heroin to be among the must important aspects of the message.

"Even under optimum circumstances, only about 10 per cent of the heroin can be eliminated by law enforcement efforts," Bourne said. The rest must be eliminated at the source of the drug in foreign countries , among them Mexico, he said.