Inspectors of the Consumer Product Safety Commission began paying visits to several children's clothing manufacturers around the country late yesterday in an attempt to determine how much clothing treated with the cancer-causing agent Tris has been exported.

Meanwhile, there have been reports that hundreds of thousands of garments, banned from Domestic sale, have been exported in recent weeks at distress prices.Alarmed by those reports, The CPSC may vote as early as today to extend the Tris ban to exports.

An attempt by commissioner Edith Barksdale Sloan to get the commission to vote yesterday failed, because at least one commissioner felt it necessary to have the advice of CPSC attorneys on the legality of the move.

That advice is expected late today in the form of a discussion of the legal arguments governing the commission's right to regulate exports of materials.

Sources at the CPSC say that the commission will probably rule that it has the right to regulate the export of any goods originally intended for sale in the United States, but that it does not have jurisdiction over clothing manufactured and labeled for export.

If that vote comes today, CPSC enforcement agents could begin seizing Tris-treated garments immediately, an action likely to set off a series of legal skirmishes between the commission and the firms which still have some of the goods on hand.

"If we wait for our legal opinion, which is only a matter of hours away, we will be on a much firmer ground," said commissioner member David Pittle.

"I thought the commission had sat on this issue long enough," said Sloan."Now we have confirmed reports of exports and we have to move in a timely manner."

She also expressed concern over reports that some of the exported garments might be coming back into the United States from a third country. CPSC staffers are checking those reports now.

The staffers are also conducting a telephone survey of about 100 manufacturers around the country to determine the location of the approximately $50 million worth of Tris-treated children's wear that firms were forced to buy back when the commission banned domestic distribution of the garments last April.

The issue of whether or not the manufacturers would be able to ship the garments overseas, where there are no bans on the treated goods, was debated heatedly until last October, when CPSC voted that it did not have the authority to stop exports.

But many of the manufacturers were unwilling to sell their goods at distress prices, partly because they hoped they would be compensated for their losses by Congress. That measure is still in the House after passing the Senate.

The manufacturers have urged that they were ordered to put Tris into children's garments by the government because the chemical is a flame retardant.

But worried about an impending export ban, several manufacturers have now begun to dump their goods. Most are getting only about one-sixth of th value of the merchandise. They say they are shipping primarily to Mxico and Venezuela.

Rep. Henry Waxman (D-Calif.) has prepared an amendment to the Consumer Product Safety Act that would give the CPSC clear authority to ban exports. Wzxman says he is irked that the commission has taken as long as it has to move on the ban.

Clothing manufacturers have told The Washington Post that "conservatively," $5 million worth of Tris-treated garments were expotee i the past ht th whiih wtule aiitu t st hte tha hals ts the eyisti 1 supply.

wwqayha has zee pteei 1 the ithhissit tt ait st ht ths whe also wrote a letter to President Carter on Feb. 9, 1978, asking for White House help in defining the CPSC role on exports