THE INTERESTING fact about President Reagan's speech in Los Angeles yesterday was that he could and did make a whole speech about arms control. This may say little about the content of his proposals or the likelihood of their passage into the form of agreements. It says a good deal about Mr. Reagan's own passage. No longer is he treating arms control as a trick that wily Soviets play on unwitting Americans. He has adopted it as an endeavor serving the country's vital security interests--not to speak of his own vital political interests. Why has he moved into an activity he tended to scorn while it was in others' hands? He observes that his proposals capitalize on the heavy arms investments he made in the first two years. He holds himself out as a steady helmsman.

A president is commonly judged to be either "for" arms control or "against" it. Neither word can possibly do justice to the complex approaches any president is required to take to issues that force themselves onto the national agenda. Yet images dominate. Mr. Reagan's image so far has been pretty bad, and he has faced a substantial vote of no confidence from the nuclear freeze movement. He renewed his criticism of the freeze yesterday--this time, wisely, identifying with its supporters' good intentions. But whether his response, or his speech as a whole, touched the emotional wellsprings of the freeze movement--the deep fear of nuclear war--is doubtful. Mr. Reagan observed that his views about the Soviet Union are well known. Unfortunately, his views about the horrors of war are still not.

The vibrancy of the war issue has ensured that some of the best minds of the country, many of them in Congress, have taken it up. A president who is eager for company on these issues does not have to rely on the simplifiers of the freeze. The single new item Mr. Reagan added to his arms control list yesterday--a call for other nuclear suppliers to adopt the same safeguards against arms diversion that the United States already has in place--has long been a congressional favorite. His pledge on the MX--to take a "fresh look"--is just the right spirit in which to approach the Hill.

The main question remains whether the president's arms and arms control policies together will make the country more secure. But the attainment of solid agreements with the Soviet Union will be one standard by which he will be judged. This puts a heavy pressure on Mr. Reagan. Most people, we believe, do not want to make the Kremlin's way any easier. But they do not want to miss any chance to reduce the danger of war.