Theories on reporter's arrest. The Daniloff dispute. Answers will shed light on nature of Gorbachev style of leadership. In Moscow, some say the KGB acted on its own in arresting Daniloff. Others say it was an effort by Kremlin hard-liners to sabotage arms control.

In 10 days, what began as a journalist's personal tragedy has become a source of superpower confrontation. The stridency of the rhetoric over the jailing of American reporter Nicholas Daniloff increased a notch yesterday. Within hours of President Reagan's remarks on the Daniloff case, the official Soviet news agency Tass published a lengthy commentary accusing the United States of using the issue to camouflage its own lack of interest in arms control.

Rhetoric and mutual accusations have tended to drown out the more basic questions surrounding the case -- questions like, who ordered Mr. Daniloff's arrested, and why?

If and when answers to these are ever found, they will shed considerable light on how the Soviet system thinks and works and on the nature of the Gorbachev era of leadership.

Most people are asking the following questions:

Why was Daniloff arrested?

Here only one answer seems plausible: The Soviets wanted to exchange him for Gennady Zakharov, a Soviet employee of the UN who was arrested on Aug. 23 and charged yesterday with espionage.

Daniloff has hinted this in phone conversations with his family and colleagues since his arrest. And the KGB, the Soviet secret police, has an outstanding track record of taking care of its own.

Who sanctioned the arrest?

There are no answers to this, only theories. One theory is that the arrest was ordered at an operational level, not from the top. This would reflect poorly on the Communist Party's ability to control the KGB, but, some Kremlin-watchers say it is plausible. The decision would still have to come pretty close to the top and is at the very least embarrassing for the senior KGB officials in the upper echelons of the party leadership.

Another theory is that the decision was approved by a depleted Politburo (it is vacation time in the Soviet Union), which blundered. We do not know, however, if a decision like this has to go to the Politburo or the Secretariat, the small group of top party leaders who handle the day-to-day business between Politburo sessions. Western Soviet-watchers are fairly evenly divided on this.

The last Politburo meeting took place Aug. 28, two days before the Daniloff arrest. One of the few things we can be reasonably confident about is that Soviet leader Mikhail Gorbachev was not there. He had gone on vacation Aug. 19, four days before Mr. Zakharov was arrested.

A number of other senior officials were probably on vacation -- including, perhaps, Andrei Gromyko, the titular head of state and a walking encyclopedia on US-Soviet relations, thanks to his 18 years as Soviet foreign minister.

But Anatoly Dobrynin -- Secretariat member, 24 years ambassador to Washington, and described recently by a fellow Central Committee member as ``our top US specialist'' -- was almost certainly in Moscow. Foreign Minister Eduard Shevardnadze and KGB chief Viktor Chebrikov were possibly there, too.

So was it a deliberate blunder, an effort by opponents of arms control to torpedo the chances of any deal with Washington?

This theory assumes that Yegor Ligachev, Mr. Gorbachev's designated No. 2, was either unable to control the rest of the leadership or that he is himself opposed to the present foreign policy. It also presupposes that the KGB is hostile to Gorbachev's policies.

Kremlin-watchers have at times thought that they detected a difference of views between Gorbachev and Mr. Ligachev. Gorbachev loyalists, however, say that the differences are ones of nuance. And far from opposing Gorbachev, the KGB is one of the new leader's strongest supporters, most foreign observers say.

How has Gorbachev reacted?

He has not cut short his vacation. His only public comments since the case began were answers to an interview with Rude Pravo, the Czechoslovak Communist Party newspaper published Monday. These made no reference to the case and largely recapitulated Gorbachev's well-known views on the need for a substantive rather than a symbolic summit.

But a well-placed Soviet source told this correspondent yesterday that the interview did contain a pressing message: that it is ``very important to keep the doors open'' in US-Soviet relations. ``People on your side and on ours'' are against improved relations, the source said, but the issues involved were too pressing to leave fallow for the next few years.

So why is Moscow acting so hard-line?

Probably because at this point it feels that it has no choice. A large amount of national prestige is involved. The case has become too big and too public for Moscow to back down.