The specter of accidentally created monsters creeping out of scientists' laboratories as a result of manipulation of human, animal and microbe genes was dealt a blow last week by six senators.

They wrote the secretary of health, education and welfare that they no longer think "recombinant DNA research" - research that can split and recombine genes - poses enough risks to make a law controlling it "absolutely necessary."

Until a few months ago, most of the six, four Democrats and two Republicans, had argued strongly in favor of such a law.

The Democrats who last week told HEW Secretary Joseph A. Califano Jr. "the need for new legislation is less clear today," are Edward M. Kennedy (Mass.), health subcommittee chairman and chief author of an originally tough, later modified control bill; Harrison A. Williams (N.J.). chairman, and Gaylord Nelson (Wis.), member of the Human Resources Committee that approved the Kennedy bill; and Adlai Stevenson (III.), science subcommittee chairman and, with Nelson, a critic of the original Kennedy bill.

The Republicans are Jacob K. Javits (N.Y.), coauthor with Kennedy of the tough approach, and Richard S. Schweiker (Pa.). ranking Minority member of the health subcommittee.

These senators last week told Califano that HEW's National Institute of Health has been commendably "cautions" in monitoring DNA research, and there has been a high level of safety" in work so far with bacterial genes.

They asked Califano if he couldn't invoke existing law to regulate such research in industry, a goal they still called necessary. And they conceded that Congress may not agree on a DNA control bill this year.

In fact, though they did not say so, efforts to pass such a law have been bogged down in the Senate by various disagreement, though prospects seem better in the House.

DNA, or deoxyribonucleic acid, is the chemical that is the basic stuff of all genes, human and animal.

The senators' letter may not end the long national debate on the safety of what is often called "gene-splitting." It was a debate that began in the spring of 1975 after scientists themselves called attention to potential dangers, such as the inadvertent creation of some new disease germ by their experimenting.

But the senators' letter is likely to create a sense of less urgency on Capitol Hill about such dangers.

Two environmental groups, Friends of the Earth and the Natural Resources Defense Fund, have been among the most vocal forces seeking strong federal and local government restraints on the work. But Nelson, one signer, is himself a leading environmentalist.

Nelson and colleagues do say safety so far has been shown in studies using a highly modified or tamed version of the human gut bacteria, E. coli. Colonies of this probably noninfectious bacteria are used as the hosts in which to cultivate various recombined genes.

The senators say "other hosts and vectors" - genes that may be split - "have recevied less scrutiny and uncertainty remains," and therefore precautions should continue.

But the senators point out that NIH officials are so confident of the work's safety to date in some 300 laboratories that they are considering extensive relaxation of their guidelines.

These would probably allow more extensive use of human, ape, monkey or other animal DNA, as well as bacteria and viruses that could lead to new vaccines or cultivation of important new drugs. The proposed revisions would probably allow extensive work on possible cancer and leukemia viruses.

NIH Director Dr. Donald Fredrickson wrote Kennedy on May 22 that some European nations are now doing research under more permissive rules, and "there is no safety advantage in having greater restrictions" here than in other nations.

The NIH guidelines none the less still apply only to federally funded research. What the senators and most scientists still want to control is research in industry, by requiring industry to follow the NIH or similar guidelines.

The senators urged Califano to try to regulate industry by using a Public Health Service act that deals with possible communicable diseases whether he will be willing to do so is highly uncertain.

On May 4 HEW Under Secretary Hale Champion told Kennedy that Califano strongly supported legislation like a House bill backed by Rep. Paul Rogers (D-Fla.), and "we do not believe" the Public Health Service law conveys "appropriate authority" to regulate the research.

For one thing, say some HEW officials, using this law might amount to admitting that DNA recombinations might cause diseases.

In any case, not much congressional motion is expected until HEW issues its revised guidelines, since Fredrickson has asked for time to do so before any new law causes him to issue regulations based on old standards.

With the urgent signal turned off in many minds, some officials and scientists now fear there may never be any action to require industry to follow safety rules.

Drugs firms have said they are voluntarily doing so. But "we really have no idea what they're doing" by way of research, an NIH official reported.