NAYPYITAW (Reuters) - A new foreign investment law should be promulgated in Myanmar soon, a senior minister said on Wednesday, after lawmakers compromised on certain proposals that were opposed by President Thein Sein who is keen to attract foreign companies.

International firms are lining up to enter Myanmar, which has opened up fast since a military regime gave way 18 months ago to the quasi-civilian government led by Thein Sein.

Western countries have lifted or suspended sanctions but most firms are waiting to see details of the investment law, which was held up in parliament for five months as proposed changes went back and forth between the assembly and the president's office.

Lawmakers approved the latest draft on September 7 and sent it back to Thein Sein for approval.

"I don't think there should be a problem. The president needs to review it. It should be ready soon," Soe Thein, a minister in the president's office, told Reuters.

Soe Thein was industry minister until promoted in late August to the president's office along with other close allies of Thein Sein. He was speaking on the sidelines of a big investment forum in the capital, Naypyitaw.

The minister's comment will soothe fears that further wrangling could delay the law until parliament reconvenes for its next session in late October.

The law as passed by parliament has not been published.

However, lawmakers have said one big change was the dropping of a proposed requirement for foreign investors to put in $5 million in start-up capital when setting up joint ventures with local partners.

Some of the changes proposed by parliament were deemed protectionist by presidential aides, who argued they would scare off foreign companies, to the benefit of the crony capitalists who dominated Myanmar's economy under the junta and remain a force.

An earlier draft had also put restrictions on 13 sectors including manufacturing, farming, agriculture and fisheries, limiting foreign firms to a maximum 49 percent of any investment there. One lawmaker said that had been altered to 50 percent.

Sources had earlier told Reuters Thein Sein wanted the start-up capital requirement dropped and the maximum foreign stake in joint ventures increased.

(Reporting by Jason Szep and Aung Hla Tun; Writing by Alan Raybould; Editing by Jeremy Laurence)