The US government's latest evidence of the use of chemical weapons in Southeast Asia has several significant immediate and longer-range effects:
* It increases the likelihood that the United States will resume producing such weapons after a 13-year hiatus in which no new stores were added to this country's chemical arsenal.
* It puts greater pressure on the United Nations to determine whether the Soviet Union and its allies are using chemical and biological weapons in Afghanistan and Southeast Asia.
* And it raises serious questions about arms control agreements generally, in particular the means by which such agreements are enforced and compliance verified.
The US State Department last week said it had found ''conclusive evidence'' that Khmer Rouge guerrillas fighting pro-Soviet forces had been attacked with toxic weapons commonly referred to as ''yellow rain.''
''Extremely high levels of toxin'' were reported found in blood samples taken by an American doctor from two Khmer Rouge subjected to an artillery attack in February.
Coincidentally, the day after this report was made public, the US Senate voted by a narrow margin (49 to 45) to approve the spending of $54 million in fiscal year 1983 to produce new chemical weapons.
While it approved the production of new binary chemical weapons (those in which the chemicals are mixed after the firing of the shell), the Senate also barred any human testing and ordered the Defense Department to dismantle existing chemical weapons at the same rate the new ones are produced.
The latest State Department evidence follows an earlier report based on cumulative data said to show that some 10,000 Laotians, Cambodians, and Afghans have been killed in hundreds of incidents dating back to 1975. State Department sources say more reports will be made as new evidence is analyzed.
''We've got an awful lot of samples under analysis, easily dozens,'' a US official said.
A United Nations team of experts reported in January that it was ''unable to reach a final conclusion'' regarding the use of chemical and biological weapons in Southeast Asia. But it did find that the nature of some injuries in that region ''could suggest a possible use of some sort of chemical-warfare agent.''
The UN voted to continue its investigation, and US officials hope their latest evidence will encourage the UN to press on.
The US data are drawing serious interest and response, even among those critical of building up US chemical weaponry. Matthew Meselson of Harvard University, who has testified against the administration on chemical arms, calls reports of their use in Afghanistan and Southeast Asia ''very disturbing.''
The 1925 Geneva Protocol prohibits the use of chemical and biological weapons , but does not bar their manufacture or stockpiling. The 1972 Biological Warfare Convention treaty bans the production of any ''bacteriological and toxin weapons.'' The United States and the Soviet Union signed both treaties.
''In the future, we must obviously insist that any new arms control agreement contain measures which ensure strict verification, and guarantee that questions of compliance are dealt with seriously,'' said Richard Burt, director of the State Department's Bureau of Politico-Military Affairs. ''We may also consider how existing arms control agreements -- not just in the chemical weapons area -- can be strengthened, both with respect to verification and compliance.''